FIELD OF INVENTION

[0001] The subject matter relates to Pd based catalyst, and in particular relates to a Pd based catalyst for oxygen reduction reaction (ORR) in an electrochemical cell.

BACKGROUND OF INVENTION

[0002] Fuel cells are highly promising energy-conversion devices due to their high efficiency and zero emission. The slackening progress of fuel cells is owing to the sluggish kinetics of oxygen reduction reaction (ORR) in the cathode part providing less power supply. Alkali mediated ORR is preferred over acid-mediated one, due to better kinetics in higher pH and less corrosive reaction condition in basic medium. Acidic media leads to the leaching of metals. Despite being the most active ORR electrocatalyst, Pt is still facing difficulties as a catalyst due to its very limited abundance and poor durability. Although recent advances are made in catalyst synthesis, such as alloy formation, intermetallic synthesis, core-shell structures, heterostructures, and shape and size control of nanoparticles, such catalysts are either not stable up to long hours or they provide large quantity of hydrogen peroxide. Selectivity towards 4e- transfer and its proper mechanistic details are yet to be achieved in alkaline media ORR.

[0003] For hastening the ORR kinetics, boosting the catalyst stability, and curbing the consumption of highly precious noble metals, various noble metal-based alloy, bimetallic, intermetallic, and heterostructures with other transition metals or non- metals are reported. Combining d-block or p-block elements with noble metals changes the d-electron occupancy of the noble metals which leads to down- or upshift of the d-band center modifying the electronic structure. The electronic structure modification improves the intermediate binding on active sites and changes the activation barrier of the reaction. The first step of ORR is 0-0 double bond cleavage which is having a bond energy of 498 kJ/mol. 0-0 bond cleavage is easier when the surface is having charge separation which polarizes the neutral O2 molecule. Commercially available Pt/C and Pd/C catalysts are well-known for ORR catalysis but face challenges of exorbitant price, less availability, and short-term stability due to OH poisoning. Many well-established Pt- or Pd-based catalysts for ORR are reported: Shape-controlled octahedral Pt-Ni alloy where annealing enhanced performance due to surface Pt enrichment, architecture control Pt-Ni nano-frames, strengthening vertex of PtCu nano frames by adding Co and forming ternary alloy PtCuCo with large stability, are some morphology -controlled highly active ORR catalysts with stability up to 10,000 ADT cycles. Interface engineering between noble metal on metal carbide, Pd/Mo2C has tuned electronic state to provide very high mass activity and onset potential but ended by having a stability of 5,000 ADT cycles. Ordered intermetallic PtFe has shown very high mass activity but with poor stability. Various metal organic framework (MOF) and covalent organic framework (COF) based systems are reported with active metal are atomically dispersed with good activity. It is very important to use a catalyst with maximum activity and stability in harsh alkaline conditions and highly selective reaction mechanisms. Therefore, there is a constant effort to obtain such catalysts for ORR to provide enhanced reaction kinetics, with a maximum production of water and minimized hydrogen peroxide as the final product.

SUMMARY OF THE INVENTION

[0004] In an aspect of the present disclosure, there is provided a catalyst of Formula I: Pt _x Pd2 xGe, wherein x is 0.1<x<0.6.

[0005] In another aspect of the present disclosure, there is provided a process for preparing the catalyst of Formula I: Pt _x Pd2- _x Ge, wherein x is 0.1<x<0.6, the process comprising: a) mixing one or more Pd precursor with one or more Pt precursor in the presence of a first solvent to obtain a first mixture; b) adding one or more Ge precursor to the first mixture under stirring followed by addition of a reducing agent to obtain a second mixture; and c) stirring and heating the second mixture to obtain the catalyst.

[0006] In a further aspect of the present disclosure, there is provided a catalyst ink comprising a) the catalyst of Formula I: Pt _x Pd2- _x Ge, wherein x is 0.1<x<0.6; b) a carbon black; and c) a binder, wherein the carbon black and the catalyst is in a weight ratio range of 1:4 to 1:6.

[0007] In one more aspect of the present disclosure, there is provided a process for preparation of a catalyst ink comprising a) the catalyst of Formula I: Pt _x Pd2- _x Ge, wherein x is 0.1<x<0.6; b) a carbon black; and c) a binder, wherein the carbon black and the catalyst is in a weight ratio range of 1:4 to 1:6, the process comprising: mixing the catalyst, the carbon black and the binder in the presence of a second solvent selected from isopropanol, water or combinations thereof to obtain the ink.

[0008] In furthermore aspect of the present disclosure, there is provided an electrode comprising a substrate and the catalyst ink comprising a) the catalyst of Formula I: Pt _x Pd2- _x Ge, wherein x is 0.1<x<0.6; b) a carbon black; and c) a binder, wherein the carbon black and the catalyst is in a weight ratio range of 1:4 to 1:6, and the catalyst ink is coated on the substrate.

[0009] In more aspect of the present disclosure, there is provided an electrochemical cell for ORR, the cell comprising: a) a working electrode comprising a substrate and the catalyst ink comprising i) the catalyst of Formula I: Pt _x Pd2- _x Ge, wherein x is 0.1<x<0.6; ii) a carbon black; and iii) a binder, the carbon black and the catalyst is in a weight ratio range of 1:4 to 1:6, the catalyst ink is coated on the substrate; b) a counter electrode; c) a reference electrode; and d) an electrolyte, wherein the cell operates in a potential range of 0.4 to 1.0 V; and the cell produces current density in a range of 5.7 to 6.0 mA/cm ² .

[0010] In one more aspect of the present disclosure, there is provided a method to reduce oxygen, the method comprising: I) de-aerating the electrochemical cell comprising: a) a working electrode comprising a substrate and the catalyst ink comprising i) the catalyst of Formula I: Pt _x Pd2- _x Ge, wherein x is 0.1<x<0.6; ii) a carbon black; and iii) a binder, the carbon black and the catalyst is in a weight ratio range of 1:4 to 1:6, the catalyst ink is coated on the substrate; b) a counter electrode; c) a reference electrode; and d) an electrolyte, by purging nitrogen through the electrolyte in the electrochemical cell to obtain a deaerated electrochemical cell; and II) providing an input feed stream of oxygen gas through the deaerated electrochemical cell operating at a potential range of 0.4 to 1.0V to reduce oxygen, wherein reducing oxygen results in production of water in a range of 98 to 99% (w/w).

[0011] The present subject matter will be better understood with reference to the following description and appended claims. This summary is provided to introduce a selection of concepts in a simplified form. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.

BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES

[0012] In order that the disclosure may be readily understood and put into practical effect, reference will now be made to exemplary embodiments as illustrated with reference to the accompanying figures. The figures together with a detailed description below, are incorporated in and form part of the specification, and serve to further illustrate the embodiments and explain various principles and advantages, in accordance with the present disclosure wherein:

[0013] Figure 1 depicts powder x-ray diffraction images of different Pt substitutions in Pd2Ge, in accordance with an embodiment of the present disclosure.

[0014] Figure 2 depicts (a) schematic representation of the synthesis of Pto.2Pd1.sGe; (b) PXRD pattern for Pto.2Pd1.sGe; (c) (111) and (210) planes of Pd2Ge; (d) Relative peak intensity ratio of (111) :(210) of Pd2Ge; (e), (f), and (g) depict the transmission electron microscopic (TEM) images, selected area electron diffraction (SAED) pattern and color mapping of Pto.2Pd1.sGe, in accordance with an embodiment of the present disclosure.

[0015] Figure 3 depicts (a), (b), scanning electron microscopic (SEM) images;(c) color mapping of Pd2Ge; (d), (e), SEM images; and (f) color mapping of Pto.2Pd1.sGe, in accordance with an embodiment of the present disclosure.

[0016] Figure 4 depicts (a) linear sweep voltammograms (LSVs) comparison of oxygen reduction reaction (ORR) for Pd2Ge, Pdi.sGe, Pto.2Pd1.sGe, and 20% Pt/C; (b) linear sweep voltammograms (LSVs) of Pto.2Pd1.sGe before and after 50,000 ADT cycles; (c) Tafel plots; (d) rotating ring disk electrode (RRDE) study of Pto.2Pd1.sGe for Pd2Ge, Pdi.sGe, Pto.2Pd1.sGe; (e) hydrogen peroxide % and no. of electrons (n) calculated values at different potentials for these catalysts; and (f) comparison of mass activity (MA) and half-wave potential (E1/2), in accordance with an embodiment of the present disclosure.

[0017] Figure 5 depicts linear sweep voltammograms (LSVs) for lower Pt- substituted Pd2Ge, in accordance with an embodiment of the present disclosure.

[0018] Figure 6 depicts LSVs at different rpm for (a) Pd2Ge; (c) Pto.2Pd1.sGe; and (e) 20% Pt/C; K-L plots for (b) Pd ₂ Ge, (d) Pto.2Pd1.sGe, and (f) 20% Pt/C, in accordance with an embodiment of the present disclosure.

[0019] Figure 7 depicts (a) No. of electron transfer (n) for three catalysts obtained from K-L plots; (b) comparison of no. of electrons transfer for Pto.2Pd1.sGe from K- L plots and RRDE experiment, in accordance with an embodiment of the present disclosure.

[0020] Figure 8 depicts (a) Methanol crossover experiment for Pto.2Pd1.sGe and 20% Pt/C; (b) ORR activity of Pto.2Pd1.sGe before and after methanol crossover experiment, in accordance with an embodiment of the present disclosure.

[0021] Figure 9 depicts projected density of states (PDOS) for (a) Pd 3d orbitals; (b) O 2p orbitals of OH adsorbed; (c) Comparison of M-0 bond length and OH poisoning effect for different catalysts; (d) Energy of OH* and OOH* adsorption on different active sites, in accordance with an embodiment of the present disclosure.

[0022] Figure 10 depicts partial density of states (PDOS) of (a) Pd2Ge; (b) Pdi.sGe; (c) Pto.2Pd1.sGe; and (d) overall comparison of PDOS, in accordance with an embodiment of the present disclosure.

[0023] Figure 11 (a-f) depicts structural models of OH* adsorbed on different active sites before and after relaxation, in accordance with an embodiment of the present disclosure.

DETAILED DESCRIPTION OF THE INVENTION

[0024] Those skilled in the art will be aware that the present disclosure is subject to variations and modifications other than those specifically described. It is to be understood that the present disclosure includes all such variations and modifications. The disclosure also includes all such steps, features, compositions, and compounds referred to or indicated in this specification, individually or collectively, and any and all combinations of any or more of such steps or features. Definitions

[0025] For convenience, before further description of the present disclosure, certain terms employed in the specification, and examples are delineated here. These definitions should be read in the light of the remainder of the disclosure and understood as by a person of skill in the art. The terms used herein have the meanings recognized and known to those of skill in the art, however, for convenience and completeness, particular terms and their meanings are set forth below.

[0026] The articles “a”, “an” and “the” are used to refer to one or to more than one (i.e., to at least one) of the grammatical object of the article.

[0027] The terms “comprise” and “comprising” are used in the inclusive, open sense, meaning that additional elements may be included. It is not intended to be construed as “consists of only”.

[0028] Throughout this specification, unless the context requires otherwise the word “comprise”, and variations such as “comprises” and “comprising”, will be understood to imply the inclusion of a stated element or step or group of element or steps but not the exclusion of any other element or step or group of element or steps. [0029] The term “including” is used to mean “including but not limited to”. “Including” and “including but not limited to” are used interchangeably.

[0030] The term “cathode” refers to an electrode where negative potential is given, and a reduction reaction takes place. The term “cathodic catalyst” refers to the catalyst which facilitates the reduction reaction in the cathode. In the present disclosure, the cathodic catalyst refers to the catalyst wherein the oxygen reduction reaction takes place.

[0031] The term “oxygen reduction reaction” (ORR) refers to the conversion reaction of oxygen to water and hydrogen peroxide. In an electrochemical cell or the fuel cell, water is preferred as a reduction product since the production of water is associated with higher current density.

[0032] The term “half-wave potential” refers to the potential required to attain half of the limiting current density obtained from the linear sweep voltammetric curve and is an indicator for evaluating an electrochemical cell’s ORR performance. Higher the half-wave potential, higher is the electrochemical performance of the cell towards ORR.

[0033] The term “current density” refers to the amount of electric current passing through per unit cross section area of the material. In the present disclosure, the current density is generated through ORR by the catalyst and is in a range of 5.7 to 6.0 mA/cm ² .

[0034] The term “mass activity” refers to the amount of current produced in the electrochemical cell with respect to the mass of the catalyst. In the present disclosure, the mass activity refers to the current generated in the electrochemical cell with respect to the mass of the Pt present in the catalyst. The mass activity denotes the efficiency of the catalyst in the oxygen reduction reaction to produce water. The mass activity of the catalyst is in a range of 300 to 350 mA/mgpt.

[0035] The term “ ADT (accelerated durability test) cycles” refers to a testing method that imparts electrochemical stress to the catalyst surface by making the catalyst surface face reduction and oxidation potential sweep in the potential window where the reaction takes place. The greater number of ADT cycles a catalyst bears without current degradation, the more is the stability of the catalyst.

[0036] The term "electrode for ORR” refers to a working electrode comprising the catalyst ink of the present disclosure with a substrate, used in the oxygen reduction reaction.

[0037] Ratios, concentrations, amounts, and other numerical data may be presented herein in a range format. It is to be understood that such range format is used merely for convenience and brevity and should be interpreted flexibly to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. For example, a weight percentage of 5-30% should be interpreted to include not only the explicitly recited limits of about 5% to 30%, but also to include sub-ranges, such as 6%, 8%, 9.4%, 15 % and so forth.

[0038] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the disclosure, the preferred methods, and materials are now described. All publications mentioned herein are incorporated herein by reference.

[0039] As discussed above, ORR (oxygen reduction reaction) results in water and hydrogen peroxide as final products via 2e“ transfer and 4e“ transfer respectively. 4e“ transfer mechanism is the most desired one in fuel cell applications since it involves higher electron transfer accompanied by the generation of a higher power. This reaction mechanism selectivity is dictated by the different ORR intermediate binding on the active sites of the catalyst. If OOH* intermediate is strongly adsorbed, peroxide desorption is not allowed. If the 0-0 bond in OOH* is made weaker, then 0-0 bond cleavage occurs leading to OH desorption and adsorbed O atom forms H2O with proton coupled electron transfer (PCET) mechanism. The stability of the catalyst depends on the OH-poisoning effect. A weakly adsorbed OH* intermediate will desorb or protonate to form water, and a strongly adsorbed one poisons the catalyst surface. Poisoning the active sites by strongly adsorbed OH is very common in Pt and Pd sites, which decreases their stability. By tuning the active sites electronically using other heteroatoms in coordination (ligand effect), the adsorption energy of OH* can be decreased and the poisoning effect can be decreased.

[0040] Intermetallic compounds are known to exhibit enhanced performance and stability. Binary compounds of Pd, such as Pd2Ge pristine system has been used for ethanol oxidation reaction (EOR) with Ni doping. The enhancement in EOR activity better than Pd/C was due to the modified electronic structure and made EOR more feasible by decreasing the energy barrier. Furthermore, it was observed that the current density of Pd2Ge in ORR was close to the state-of-the-art Pt/C catalyst. The inventors focussed on the selective substitution of Pd sites for enhancing the onset potential close to the theoretical value with the maximum electron (4e-) transfer process. Accordingly, the present disclosure provides a catalyst of Formula I: Pt _x Pd2- _x Ge wherein x is 0. l<x<0.6. In this catalyst, Pd-vacancies were generated, and those sites are substituted with Pt atoms site selectively. Pt substituted Pd2Ge was observed to exhibit much better performance than Pt and it was found to be highly stable in ORR conditions with no poisoning. The catalyst of the present disclosure also provides the highest production of water with minimum of hydrogen peroxide, thereby generating higher current density.

[0041] In an embodiment of the present disclosure, there is provided a catalyst of Formula I: Pt _x Pd2- _x Ge, wherein x is 0. l<x<0.6. In another embodiment of the present disclosure, x is 0.2.

[0042] In an embodiment of the present disclosure, there is provided a catalyst of Formula I: Pt _x Pd2- _x Ge as disclosed herein, wherein the catalyst is a cathodic catalyst for oxygen reduction reaction (ORR).

[0043] In another embodiment of the present disclosure, there is provided a catalyst of Formula I: Pt _x Pd2- _x Ge, wherein x is 0.1<x<0.6 and the catalyst is a cathodic catalyst for oxygen reduction reaction (ORR).

[0044] In an embodiment of the present disclosure, there is provided a catalyst of Formula I as disclosed herein, wherein the catalyst exhibits half-wave potential in a range of 0.4 to 1.0 V, stability up to 50,000 ADT cycles; current density in a range of 5.7 to 6 mA/cm ² ; and mass activity in a range of 300 to 350 mA/mgpt. In another embodiment of the present disclosure, wherein the catalyst exhibits half-wave potential in a range of 0.7 to 1.0 V, stability up to 50,000 ADT cycles; current density in a range of 5.7 to 6 mA/cm ² ; and mass activity in a range of 310 to 340 mA/mgpt. In yet another embodiment of the present disclosure, the catalyst exhibits half-wave potential in a range of 0.9 to 1.0 V, stability up to 50,000 ADT cycles; current density in a range of 5.7 to 6 mA/cm ² ; and mass activity of 320 mA/mgpt.

[0045] In an embodiment of the present disclosure, there is provided a catalyst of Formula I as disclosed herein, wherein the catalyst has a particle size in a range of 20 to 25 nm.

[0046] In an embodiment of the present disclosure, there is provided a catalyst of Formula I as disclosed herein, wherein the catalyst catalyzes ORR to produce water in a range of 98 to 99% (w/w) with respect to the weight of input gas stream of oxygen.

[0047] In an embodiment of the present disclosure, there is provided a cathodic catalyst of Formula I: Pt _x Pd2- _x Ge, wherein x is 0.2 with particle size in a range of 20 to 25 nm, wherein the catalyst exhibits half-wave potential in a range of 0.4 to 1.0 V, stability up to 50,000 ADT cycles; current density in a range of 5.7 to 6 mA/cm ² ; mass activity in a range of 300 to 350 mA/mgpt; and catalyzes ORR to produce water in a range of 98 to 99% (w/w).

[0048] In an embodiment of the present disclosure, there is provided a process for preparing the catalyst of Formula I: Pt _x Pd2- _x Ge, wherein x is 0.1<x<0.6, the process comprising: a) mixing one or more Pd precursor with one or more Pt precursor in the presence of a first solvent to obtain a first mixture; b) adding one or more Ge precursor to the first mixture under stirring followed by addition of a reducing agent to obtain a second mixture; and c) stirring and heating the second mixture to obtain the catalyst. In another embodiment of the present disclosure, wherein adding one or more Ge precursor to the first mixture was carried out under stirring for a time period of 30 minutes.

[0049] In an embodiment of the present disclosure, there is provided a process for preparing the catalyst of Formula I as disclosed herein, wherein stirring the second mixture is carried out for a time period in a range of 20 to 60 minutes; and heating the second mixture is carried out at a temperature in a range of 200 to 250°C for a time period in a range of 22 to 26 hours. In another embodiment of the present disclosure, wherein stirring the second mixture is carried out for a time period in a range of 30 to 45 minutes; and heating the second mixture is carried out at a temperature of 220°C for a time period of 24 hours.

[0050] In an embodiment of the present disclosure, there is provided a process for preparing the catalyst of Formula I as disclosed herein, wherein the Pd precursor and the Ge precursor is taken in the mole ratio range of 2.2:1 to 1.2:1. In another embodiment of the present disclosure, wherein the Pd precursor and the Ge precursor is taken in the mole ratio range of 2:1 to 1.4:1. In yet another embodiment of the present disclosure, the Pd precursor and the Ge precursor is taken in the mole ratio of 1.8:1.

[0051] In an embodiment of the present disclosure, there is provided a process for preparing the catalyst of Formula I as disclosed herein, wherein the Pt precursor is taken in a weight range of 5 to 30% by weight of the Pd precursor. In another embodiment of the present disclosure, wherein the Pt precursor is taken in a weight range of 7 to 25% by weight of the Pd precursor. In one another embodiment of the present disclosure, wherein the Pt precursor is taken in a weight range of 8 to 15% by weight of the Pd precursor. In further another embodiment of the present disclosure, the Pt precursor is taken in 10% by weight of the Pd precursor.

[0052] In an embodiment of the present disclosure, there is provided a process for preparing the catalyst of Formula I as disclosed herein, wherein the Pd precursor is selected from K^PdCU, PdCh, Pd(acac)2, or combinations thereof; the Ge precursor is selected from GcCU. Gch, or combinations thereof; and the Pt precursor is K^PtCk In another embodiment of the present disclosure, the Pd precursor is K^PdCU, and the Ge precursor is GcCU-

[0053] In an embodiment of the present disclosure, there is provided a process for preparing the catalyst of Formula I as disclosed herein, wherein the first solvent is selected from ethylene glycol, triethylene glycol, or tetraethylene glycol or combinations thereof. In another embodiment of the present disclosure, wherein the first solvent is triethylene glycol.

[0054] In an embodiment of the present disclosure, there is provided a process for preparing the catalyst of Formula I as disclosed herein, wherein the reducing agent is selected from superhydride, sodium borohydride (NaBFU), or oleyl amine-oleic acid. In another embodiment of the present disclosure, the reducing agent is selected from superhydride (Li(C2Hs)3BH).

[0055] In an embodiment of the present disclosure, there is provided a process for preparing the catalyst of Formula I as disclosed herein, wherein the Pd precursor is selected from K^PdCU, PdCh, Pd(acac)2, or combinations thereof; the Ge precursor is selected from GcCU. Geh, or combinations thereof; the Pt precursor is K^PtCU; the first solvent is selected from ethylene glycol, triethylene glycol, or tetraethylene glycol or combinations thereof; and the reducing agent is selected from superhydride, sodium borohydride (NaBFU), or oleyl amine-oleic acid. In another embodiment of the present disclosure, the Pd precursor is K^PdCU; the Ge precursor is GcCU: the Pt precursor is K^PtCU; the first solvent is ethylene glycol, and the reducing agent is superhydride. [0056] In an embodiment of the present disclosure, there is provided a process for preparing the catalyst of Formula I as disclosed herein, wherein the Pd precursor is selected from K2PdC14, PdCh, Pd(acac)2, or combinations thereof; the Ge precursor is selected from GcCU. GeF, or combinations thereof; the Pt precursor is K2PtC14 _; wherein the Pd precursor and the Ge precursor is taken in the mole ratio range of 2.2:1 to 1.2:1; and the Pt precursor is taken in weight range of 5 to 30% by weight of the Pd precursor.

[0057] In an embodiment of the present disclosure, there is provided a process for preparing the catalyst of Formula I as disclosed herein, the process comprising: a) mixing Pd precursor selected from K2PdC14, PdCh, Pd(acac)2, or combinations thereof, with K2PtC14 in the presence of triethylene glycol to obtain a first mixture; b) adding Ge precursor selected from GcCU. Gek, or combinations thereof, to the first mixture under stirring for 30 minutes followed by addition of a reducing agent selected from superhydride, sodium borohydride (NaBFU), or oleyl amine-oleic acid to obtain a second mixture; and c) stirring for a time period in a range of 20 to 60 minutes and heating the second mixture at a temperature in a range of 200 to 250°C for a time period in a range of 22 to 26 hours to obtain the catalyst, wherein the Pd precursor and the Ge precursor is taken in a mole ratio range of 2.2:1 to 1.2:1; and the Pt precursor is taken in a weight range of 5 to 30% by weight of the Pd precursor. [0058] In an embodiment of the present disclosure, there is provided a catalyst ink comprising a) the catalyst of Formula I Pt _x Pd2- _x Ge, wherein x is 0.1<x<0.6; b) a carbon black; and c) a binder, wherein the carbon black and the catalyst is in a weight ratio range of 1 :4 to 1 :6. In another embodiment of the present disclosure, the carbon black and the catalyst is in a weight ratio of 1:5.

[0059] In an embodiment of the present disclosure, there is provided a process for preparation of a catalyst ink comprising a) the catalyst of Formula I Pt _x Pd2- _x Ge, wherein x is 0.1<x<0.6; b) a carbon black; and c) a binder, wherein the carbon black and the catalyst is in a weight ratio range of 1:4 to 1:6, the process comprising: mixing the catalyst, the carbon black and the binder in the presence of a second solvent selected from isopropanol, water, or combinations thereof to obtain the ink. [0060] In an embodiment of the present disclosure, there is provided an electrode comprising a substrate and the catalyst ink comprising a) the catalyst of Formula I Pt _x Pd2-xGe, wherein x is 0.1<x<0.6; b) a carbon black; and c) a binder, wherein the carbon black and the catalyst is in a weight ratio range of 1:4 to 1:6, and the catalyst ink is coated on the substrate.

[0061] In an embodiment of the present disclosure, there is provided an electrode comprising a substrate and the catalyst ink comprising a) the catalyst of Formula I Pt _x Pd2 xGe, wherein x is 0.1<x<0.6; b) a carbon black; and c) a binder, wherein the carbon black and the catalyst is in a weight ratio range of 1:4 to 1:6, the catalyst ink is coated on the substrate; and the substrate is glassy carbon. In another embodiment of the present disclosure, the electrode comprises a teflon insulating with centre glass carbon coated with the catalyst ink. In yet another embodiment of the present disclosure, the electrode is a rotating-ring disk electrode.

[0062] In an embodiment of the present disclosure, there is provided an electrochemical cell for ORR, the cell comprising: a) a working electrode comprising a substrate and the catalyst ink comprising i) the catalyst of Formula I Pt _x Pd2- _x Ge, wherein x is 0. l<x<0.6; ii) a carbon black; and iii) a binder, the carbon black and the catalyst is in a weight ratio range of 1:4 to 1:6, the catalyst ink is coated on the substrate; b) a counter electrode; c) a reference electrode; and d) an electrolyte, wherein the cell operates in a potential range of 0.4 to 1.0 V; and the cell produces current density in a range of 5.7 to 6.0 mA/cm ² . In another embodiment of the present disclosure, active surface area of the electrode is 0.0706 cm ² .

[0063] In an embodiment of the present disclosure, there is provided an electrochemical cell for ORR as disclosed herein, wherein the counter electrode is graphite rod; the reference electrode is mercury /mercuric oxide electrode or calomel electrode; and the electrolyte is potassium hydroxide or perchloric acid. In another embodiment of the present disclosure, wherein the reference electrode is mercury /mercuric oxide electrode with alkaline electrolyte potassium hydroxide or calomel electrode with acidic electrolyte perchloric acid. In yet another embodiment of the present disclosure, the electrolyte is 0.1M potassium hydroxide or 0.1M perchloric acid. In further another embodiment of the present disclosure, the electrolyte acts as a source of hydrogen in the oxygen reduction reaction.

[0064] In an embodiment of the present disclosure, there is provided an electrochemical cell for ORR as disclosed herein, wherein the working electrode is rotating-ring disk electrode, rotating at a speed in a range of 80 to 2600 rpm. In another embodiment of the present disclosure, wherein the working electrode rotates at a speed in a range of 100 to 2500 rpm. In yet another embodiment of the present disclosure, the working electrode rotates at a speed in a range of 1000 to 2500 rpm. [0065] In an embodiment of the present disclosure, there is provided an electrochemical cell for ORR as disclosed herein, wherein the cell is stable up to 50000 ADT cycles.

[0066] In an embodiment of the present disclosure, there is provided an electrochemical cell for ORR, the cell comprising: a) a glassy carbon electrode comprising the catalyst ink comprising i) the catalyst of Formula I Pt _x Pd2- _x Ge, wherein x is 0.1<x<0.6; ii) vulcan black; and iii) nafion, the carbon black and the catalyst is in a weight ratio range of 1 :4 to 1:6, the catalyst ink is coated on the glassy carbon; b) graphite rod as counter electrode; c) mercury /mercuric oxide electrode or calomel electrode as reference electrode; and d) potassium hydroxide or perchloric acid as electrolyte, wherein the cell operates in a potential range of 0.4 to 1.0 V; the cell produces current density in a range of 5.7 to 6.0 mA/cm ² ; and the cell is stable up to 50000 ADT cycles.

[0067] In an embodiment of the present disclosure, there is provided an electrochemical cell for ORR, the cell comprising: a) a glassy carbon electrode coated with the catalyst ink comprising i) the catalyst of Formula I Pt _x Pd2- _x Ge, wherein x=0.2; ii) vulcan black; and iii) nafion, the carbon black and the catalyst is in a weight ratio of 1:5; b) graphite rod as counter electrode; c) mercury /mercuric oxide electrode as reference electrode; and d) potassium hydroxide as electrolyte, wherein the cell operates in a potential range of 0.4 to 1.0 V; and the cell produces current density in a range of 5.7 to 6.0 mA/cm ² ; and the cell is stable up to 50000 ADT cycles. [0068] In an embodiment of the present disclosure, there is provided an electrochemical cell for ORR, the cell comprising: a) a glassy carbon electrode coated with the catalyst ink comprising i) the catalyst of Formula I Pt _x Pd2- _x Ge, wherein x=0.2; ii) vulcan black; and iii) nafion, the carbon black and the catalyst is in a weight ratio of 1:5; b) graphite rod as counter electrode; c) calomel electrode as reference electrode; and d) perchloric acid as electrolyte, wherein the cell operates in a potential range of 0.4 to 1.0 V; the cell produces current density in a range of 5.7 to 6.0 mA/cm ² ; and the cell is stable up to 50000 ADT cycles.

[0069] In an embodiment of the present disclosure, there is provided a method to reduce oxygen, the method comprising: I) de-aerating the electrochemical cell comprising: a) a working electrode comprising a substrate coated with the catalyst ink comprising i) the catalyst of Formula I Pt _x Pd2- _x Ge, wherein x is 0. l<x<0.6; ii) a carbon black; and iii) a binder, the carbon black and the catalyst is in a weight ratio range of 1:4 to 1:6; b) a counter electrode; c) a reference electrode; and d) an electrolyte, by purging nitrogen through the electrolyte in the electrochemical cell to obtain a deaerated electrochemical cell; and II) providing an input feed stream of oxygen gas through the deaerated electrochemical cell operating at a potential range of 0.4 to 1.0V to reduce oxygen, wherein reducing oxygen results in production of water in a range of 98 to 99% (w/w).

[0070] In an embodiment of the present disclosure, there is provided a method to reduce oxygen, the method comprising: I) de-aerating the electrochemical cell comprising: a) a working electrode comprising a substrate coated with the catalyst ink comprising i) the catalyst of Formula I Pt _x Pd2- _x Ge, wherein x=0.2; ii) a carbon black; and iii) a binder, the carbon black and the catalyst is in a weight ratio of 1:5; b) graphite rod as counter electrode; c) mercuric/ mercuric oxide as reference electrode; and d) potassium hydroxide as electrolyte, by purging nitrogen through potassium hydroxide in the electrochemical cell to obtain a deaerated electrochemical cell; and II) providing an input feed stream of oxygen gas through the deaerated electrochemical cell operating at a potential range of 0.4 to 1.0V to reduce oxygen, wherein reducing oxygen results in production of water in a range of 98 to 99% (w/w). In another embodiment of the present disclosure, there is provided a method to reduce oxygen, the electrolyte is perchloric acid with calomel electrode as reference electrode.

[0071] Although the subject matter has been described in considerable detail with reference to certain examples and implementations thereof, other implementations are possible.

EXAMPLES

[0072] The disclosure will now be illustrated with working examples, which are intended to illustrate the working of disclosure and not intended to take restrictively to imply any limitations on the scope of the present disclosure. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this disclosure belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice of the disclosed methods and compositions, the exemplary methods, devices, and materials are described herein. It is to be understood that this disclosure is not limited to particular methods, and experimental conditions described, as such methods and conditions may apply.

[0073] The working examples described herein provide a catalyst of Formula I Pt _x Pd2- _x Ge wherein x is 0.1<x<0.6. The present disclosure also provides a process for preparing the catalyst. Pd2Ge crystallizes in the ordered hexagonal structure (space group: P62m). The catalyst of Formula I was synthesized via solvothermal method. By reducing the Pd precursor content from the stoichiometric composition, a Pd deficient system (for example-Pdi.sGe) was produced, which was then filled with an equivalent amount of Pt atoms (Pto.2Pd1.sGe). The present disclosure also provides a catalyst ink comprising the catalyst of Formula I with carbon black and a binder. The present disclosure further provides a working electrode comprising the catalyst of Formula I coated on a conducting substrate. The working electrode is employed in an electrochemical cell with three electrode setup, wherein the oxygen reduction reaction was carried out. The forthcoming examples illustrate the aspects of the present disclosure in further detail.

Materials and Methods [0074] All the chemicals were obtained from high grade certified reagent houses and were used without further purification. Potassium tetra chloropalladate (K^PdCU), and germanium (IV) chloride (GcCL) were procured from Alfa Aesar, superhydride solution (reducing agent) and triethylene glycol from Merck, vulcan black from fuel cell store, nafion from sigma Aldrich and potassium hydroxide from SDFCL.

[0075] K2PtC14 was obtained from Alfa Aesar Premion®, of purity 99.99%. Oxygen gas of purity 99.999 % was purchased from Spec & Cal Pvt. Ltd . The gas flow inside the electrochemical cell was controlled by RRDE set-up with a pressure of around 1-2 bar and a very low flow of gas (5 cm ³ /min) was maintained throughout the experiment.

[0076] The catalyst of the present disclosure was characterized by powder X-ray diffraction (PXRD), scanning electron microscopic analysis (SEM), transmission electron microscopic analysis (TEM) and high-resolution TEM (HRTEM and selected area electron diffraction (SAED).

[0077] Powder X-ray Diffraction (PXRD) measurements were done at room temperature on a Rigaku Miniflex X-ray diffractometer with Cu-Ka X-ray source (A = 1.5406 A), equipped with a position sensitive detector in the angular range 20° < 29 < 80° with the step size 0.02° and scan rate of 0.5 s/step calibrated against corundum standards.

[0078] The SEM measurement was performed using Leica scanning electron microscopy equipped with an energy-dispersive X-ray spectroscopy (EDAX) instrument (Bruker 120 eV EDAX instrument). Data were acquired by using an accelerating voltage of 15 kV, and the typical time taken for data accumulation is 100 s. The elemental analyses were performed using the P/B-ZAF standardless method (where P/B = peak to background model, Z = atomic no. correction factor, A = absorption correction factor, and F = fluorescence factor) for Cu, Ga at multiple areas on the sample coated Si wafer.

[0079] TEM and high -resolution TEM (HRTEM) images, selected area electron diffraction (SAED) patterns were collected using a JEOL 200 TEM instrument. Samples for these measurements were prepared by dropping a small volume of sonicated ethanolic dispersion onto a carbon-coated copper grid. [0080] Theoretical (Density Functional Theoretical) calculations were performed using PWSCF v.5.1 code embedded in Quantum Espresso suite for quantum simulation of materials. The PWSCF calculations were performed using generalized gradient approximation (GGA) with PBE exchange correlation functional and ultrasoft pseudopotential. Kinetic energy (Ek) cut-off for the wavefunctions of 60.0 Ry was used to truncate the plane-wave basis. Furthermore, Gaussian smearing was used with a degauss value of 0.005 Ry. Systems were relaxed until S4 the Hellmann-Feynman forces on each atom are in the order of 10-2-10-3 eV/A. The calculated Fermi energy (Ef) was set to zero for all the DOS plots. A vacuum of 14 A was used to avoid any interaction among the slabs.

Example 1

Preparation of the catalyst

[0081] The catalyst was synthesized by solvothermal method. 0.2 mmol of potassium tetra chloropalladate (K2PdC14), and 0.1 mmol of germanium(IV) chloride (GcCE) for Pd2Ge, and 0.8 mL of superhydride solution (reducing agent) were mixed in 16 mL of triethylene glycol (TEG) and was heated in autoclaves at 220 °C for 24 hours to obtain Pd2Ge. Pd2Ge was prepared for a comparative analysis of the catalyst of the present disclosure.

[0082] In an actual preparation of the catalyst of Formula I with x=0.2, 0.18 mmol of K2PdC14 was taken with 0.02 mmol of K2PtC14 in the presence of 16 ml of TEG under stirring to obtain a first mixture. To this first mixture, 11.4 ml of 0.1 mmol of germanium(IV) chloride (GcCL) was added under stirring followed by the addition of 0.8 mL of superhydride solution (Li(C2Hs)3BH) to obtain a second mixture. This second mixture was kept under continuous stirring for a time period of 30 to 45 minutes and then heated in autoclave at 220 °C for 24 hours to obtain the catalyst. Similarly, the catalyst of Formula I wherein x=0.1, 0.4, 0.6 was prepared by taking 0.19 mmol, 0.16 mmol, and 0.14 mmol of K2PdC14, respectively with subsequent 0.01 mmol, 0.04 mmol, and 0.06 mmol of K2PtC14, respectively.

[0083] When x=0.2, 0.02 mmol of K2PtC14 was found to provide 10% by weight of Pt with respect to % weight of Pd in the catalyst. Similarly, 0.01 mmol, 0.04 mmol, and 0.06 mmol of K^PtCU corresponded to 5% 8% and 12% by weight of Pt with respect to % weight of Pd in the catalyst.

[0084] In the process of preparing the catalyst, reducing agents such as sodium borohydride (NaBFU), or oleyl amine-oleic acid can be used. Among Pt, Pd and Ge, Ge has the least tendency to reduce. So, a strong reducing agent such as superhydride was required to reduce Ge along with Pd so that proper diffusion of Pt, Pd, and Ge takes place resulting in the intermetallic formation of the catalyst of Formula I. With a weak reducing agent, Pd reduced faster to form Pd nanoparticles and the intermetallic phase was not obtained.

[0085] The present disclosure illustrates a solvothermal method for the preparation of the catalyst, however other methods such as colloidal synthesis, vapor phase synthesis, electrosynthesis (via electrodeposition), and solid-state synthesis at high temperature may also be deployed.

Example 2

Characterization of the catalyst

[0086] The catalyst prepared in example 1 was subjected to powder x-ray diffraction analysis. Figure 1 depicts the schematic PXRD pattern showing the atomic arrangement of Pd, Ge and Pt in Pd2Ge, Pdi.sGe and Pto.2Pd1.sGe system. Figure la depicts the PXRD pattern in the 29 range of 20 to 90 °, and Figure lb depicts the specific pattern in 29 range of 35 to 45. The absence of any shift in the XRD pattern with respect to Pd2Ge, clearly confirmed no inherent vacancy was present in pristine Pd2Ge. The substitution of Pt done on the compounds Pd2Ge and Pdi.sGe and the absence of any shift in XRD clarified that Pt having higher reduction potential reduced faster than Pd and occupied Pd positions even though Pd was present in excess. The substitution of higher amount of Pt was not successful as it led to formation of Pt nanoparticles as shown with a minor peak 29 = 49°. Therefore, an optimal substitution of Pt in Formula I having x in a range of 0.1 to 0.6 resulted in a catalyst with improved structural and catalytic properties.

[0087] Figure 2a illustrates the schematic representation of synthesis of the catalyst of Formula I Pto.2Pd1.sGe. The PXRD pattern (Figure 2b) showed a right shift of major peak corresponding to (111) plane signifying lattice contraction due to Pd atom vacancies created in Pdi.sGe and the left shift of the peak after Pt substitution signified the lattice expansion due to larger Pt atoms substituting Pd atoms. The crystallographic plane (111) was terminated by both Pt and Ge atoms, whereas (210) plane was terminated mainly by Ge atoms with some Pt atoms, which partially occupied the facet (210), as shown in Figure 2c. It was expected that if Pt atoms are substituting selectively the Pd atoms, not only the peak positions would change but peak intensity would also increase due to higher electron-dense Pt atoms. Such change may not be observed in the plane (210) which has only Ge atoms. To assess this, relative peak intensity ratio of (111):(210) was calculated for Pd2Ge, Pdi.sGe, and Pto.2Pd1.sGe. It was observed that upon Pd deficiency the (111):(210) ratio had been increased, and upon Pt substitution the ratio had increased (as in Figure 2d). This clearly confirmed that Pt had been substituted at Pd sites.

[0088] Transmission electron microscopic (TEM) images in Figure 2e showed network-like connected nanospheres of Pd2Ge with 20 nm diameter. Selected-area electron diffraction (SAED) pattern in Figure 2f showed the major peaks exposed were (111) and (210). Finally, elemental distribution by color-mapping in Figure 2g confirmed the uniform distribution of metals. Scanning electron microscopic (SEM) images and energy-dispersive X-ray (EDX) color mapping images are shown in Figure 3 (a), (b), and (c) are SEM images and color mapping of Pd2Ge, and (d), (e), and (f) are SEM images and color mapping of Pto.2Pd1.sGe.

Example 3

Preparation of catalyst ink and an electrode

[0089] The catalyst prepared in example 1 was used to prepare the catalyst ink. The catalyst ink was prepared by mixing 2 mg of the catalyst with 0.4 mg vulcan black in 600 pl of second solvent (isopropanol: water in 1 : 1) and 20 pL of 1 wt.% Nafion as binder. 5 pL of the catalyst ink was drop cast on the commercial 3 mm glassy carbon electrode and was used as a working rotating disk electrode (RDE). The active electrode surface area coated with the catalyst was found to be 0.0706 cm ² .

Example 4

Electrochemical Oxygen Reduction Reaction [0090] All the electrochemical measurements were done in an electrochemical cell with 3-electrode set-up comprising of a rotating disk electrode (RDE) as the working electrode, graphite rod as counter electrode, and mercury /mercuric oxide electrode (MMO) with potassium hydroxide as the electrolyte. Commercial Pt/C (20 wt.%, Sigma Aldrich) was used for comparison of activity. Polarization curves were the anodic sweep of the cyclic voltammograms (CVs) recorded for ORR at a scan rate of 5 mV s’ ¹ at 25 °C in the potential range of 0.4 V to 1.0 V vs. RHE rotating the RDE at 100, 225, 400, 625, 900, 1225, 1600, 2025, and 2500 rpm.

[0091] The electrolyte solution of 0.1 M potassium hydroxide in the electrochemical was deaerated by purging nitrogen gas into the solution at least for 30 min to obtain the deaerated electrochemical cell and this N2 saturated CV was conducted on the deaerated electrochemical cell. Further, O2 gas was purged for an hour through the deaerated electrochemical cell and CVs were taken with the cell operating in the potential in a range 0.4 to 1.0V to reduce oxygen. The electrolyte acts as a source of hydrogen which facilitates the reduction of oxygen to obtain water and hydrogen peroxide as the final products. The electrochemical set up comprising RRDE used in the present disclosure in which the oxygen gas flow can be controlled and was kept at 20 seem (standard cubic centimetres per minute) O2 flow. The exact flow to the electrode surface varied with the rpm of RDE rotation. The more the rotation, the more was the flow near the electrode surface.

[0092] The polarization curves in N2 and O2 saturated solutions were taken in 1600 rpm rotating speed of RDE. Accelerated degradation tests of 50,000 cycles were conducted in the potential range of 0.7 V to 1.0 V vs. RHE with scan rate of 50 mV/sec. Electrochemical impedance studies were performed in the frequency range from 10 mHz to 100 kHz at different applied DC potentials for different reactions depending on their onset potential values. The reference electrode MMO was calibrated with respect to the reversible hydrogen electrode (RHE), using Pt as working and counter electrodes in 0.1 M KOH solution. The calibrated value obtained for 0.1M KOH alkaline medium was ERHE = EMMO + 0.911 V and the calibrated reference electrode MMO was used for the electrochemical study using the electrode of the present disclosure as the working electrode. [0093] ORR activity was checked in alkaline media (0.1 M KOH) using Pd2Ge, the deficient (Pdi.sGe) and Pt substituted (Pto.2Pd1.sGe) as catalysts and their performances were compared with the state-of-the-art catalyst, commercially available 20% Pt/C (Figure 4a). It was found that pristine Pd2Ge and Pto.2Pd1.sGe produced a current density of 5.7 mA/cm ² which was similar to as obtained for commercial catalyst 20% Pt/C.

[0094] From the linear sweep voltammograms (LSVs), it was observed that after creating Pd deficiencies there was a drop in current density as well as in the onset and half-wave potentials which firmly confirmed that Pd atoms were the main active sites. After substituting Pd atoms by Pt atoms, the overpotential decreased and halfwave potential increased to 0.94 V vs. RHE, though there was no increase or decrease in current density as compared to pristine Pd2Ge catalyst. This strongly supported that with substitution there had been a modification in the electronic structure of Pd atoms (the active sites), which drove the ORR kinetics faster and more feasible.

[0095] Furthermore, the Pt substituted catalyst exhibits excellent stability of 50,000 ADT cycles (Figure 4b). The Tafel-slope for Pto.2Pd1.sGe was the lowest for both the onset potential region and half-wave potential region, which were 41.3 and 111.09 mV/dec, respectively (Figure 4c). The lowest Tafel-slope value signified faster charge transfer from active sites to intermediate species (O2 to form superoxide (O2 ) radical) with optimum adsorption and easy desorption of intermediates. A decreasing trend in the Tafel slope value from pristine to the catalyst of Formula I indicated that Pt substitution increased the electron density on Pd atom and induced strain in the catalyst. Pt substitution also modified the metal-metal bond distance of catalyst, which further modified active metal-0 bond strength.

[0096] ORR performed using rotating ring disk working electrode (RRDE) comprising the catalyst Pto.2Pd1.sGe was performed, which produced only 1.4% of H2O2 (Figure 4d) and 98.6% of water. The number of electron transfers were calculated and was found to be in a range of 3.97 to 4 in the entire potential range for Pto.2Pd1.sGe (Figure 4e). Figure 5 depicts the linear sweep voltammograms (LSVs) for lower Pt-substituted Pd2Ge. It was understood from LSVs that when Pt was loaded in 2.5 to 5% by weight with respect to the weight of Pd, the catalyst did not show any significant improved catalytic performance. This was because required Pt incorporation in the catalyst was not attained to form sufficient Pd-Pt bonds which is the key reason behind the charge transfer during ORR for enhancing the kinetics. Beyond 5% by weight of Pt, the incorporation of Pt in the catalyst was achieved thereby exhibiting improved catalytic performance.

[0097] Figure 6 depicts the LSVs at different rpm for (a) Pd2Ge, (c) Pto.2Pd1.sGe, and (c) 20% Pt/C and the number of electron transfers were calculated from K-L plots as depicted in Figure 6 (b) Pd2Ge, (d) Pto.2Pd1.sGe, and (f) 20% Pt/C.

[0098] As shown in Figure 7a, as per K-L plot, the catalyst with the highest selectivity of 4e- transfer was found to be Pto.2Pd1.sGe. The results obtained from RRDE, and K-L plots were similar as depicted in Figure 7b. The mass activity of the catalyst Pto.2Pd1.sGe was found to be 322 mA mg ^-1 pt with respect to Pt mass loading, which was almost 3 times higher than that of commercial catalyst 20% Pt/C. In addition, negligible change in mass activity after 50,000 ADT cycles confirmed excellent stability (Figure 4f). The comparison of half-wave potential for all Pd-Ge- based catalysts of Formula I and Pt/C are shown in Figure 4f further confirming that Pto.2Pd1.sGe provided improved results.

[0099] Methanol crossover experiment convinced that Pto.2Pd1.sGe was methanol- tolerant without showing any change in ORR current density (as in Figure 8a) and Pt/C was giving a transition from negative to positive current density corresponding to methanol oxidation reaction by Pt/C. The catalyst Pto.2Pd1.sGe showed that there was no degradation in E1/2 value even after injecting methanol (as in Figure 8b). In general, direct methanol fuel cells (DMFCs), ORR and methanol oxidation reactions are the cathodic and anodic reactions where the two chambers are separated by anion exchange membrane. Commonly, methanol crosses over the membrane from anodic to the cathodic chamber. This methanol affects the ORR kinetics in the cathode chamber if the cathode is Pt due to CO-poisoning during methanol oxidation. This leads to decreased stability of the cathode in real-life fuel cell applications. However, in the present disclosure, the catalyst Pto.2Pd1.sGe did not show any change in its performance even after methanol was injected into ORR reaction conditions, indicating the improved stability over other catalysts for ORR kinetics.

[00100] Despite the availability of lots of catalysts for ORR, the main challenge that remained was the selectivity of reaction mechanism proceeding via 4e“ transfer for the production of water. The formation of water from molecular O2 was dependent on the feasibility of 0-0 bond cleavage which can be facilitated by strong adsorption on the active site and charge polarization on the catalyst surface that would easily polarize the electron cloud of the stable and neutral molecule. If the 0-0 cleavage occurred less, the ORR proceeded via 2e“ pathway forming hydrogen peroxide. However in the present disclosure, it was observed that negligible H2O2 was formed in electrochemical measurements, some computational insight was conducted to understand the catalytic phenomena.

Example 5

Density Functional Theoretical calculations

[00101] Partial density of states (PDOS) for Pd 3d orbitals was calculated for Pd2Ge, Pdi.sGe and Pto.2Pd1.sGe catalysts. Fermi level measures the equilibrium electronic energy of a solid material. As seen in Figure 9a, the electron density of Pd 3d orbitals was closer to the Fermi level in Pto.2Pd1.sGe as compared to the pristine and deficient systems, which resulted in strong interaction between the catalyst active site (Pd atoms) and the adsorbate (O2 & H2) molecules. The contribution of electrons of Pd 3d orbital to the density of states (DOS) means electrons of Pd 3d orbitals are in the conduction band and takes part in the reduction reaction. Therefore, the electron accumulation on Pd sites helped in enhancing the ORR kinetics.

[00102] Comparing the total-DOS for 111 slabs of Pd2Ge, Pdi.sGe, and Pto.2Pd1.sGe, it was observed that after substituting there is an overall increase in the electron density near the Fermi level (Figures 9a-d). Figure 9c showed the trend of decreasing OH* poisoning with increasing metal-0 bond distance of OH* species on the catalyst surface. The absorption energies of OH* and OOH* on various active sites for the catalysts are calculated and plotted in Figure 9d. It was seen that OH* is weakly adsorbed on Pd and Pt sites of Pto.2Pd1.sGe than on Pd2Ge, which means Pto.2Pd1.sGe catalyst is least poisoned. Whereas OOH* species is strongly bounded in Pto.2Pd1.sGe than in pristine PchGc. The weaker binding of OOH* on surface sites is a bane for 4e- transfer ORR mechanism leading to the formation of a large percentage of H2O2. If OOH* is strongly bound, the tendency of peroxide anion release from catalyst surface will be less, and further 2e- transfer will take place on absorbed OOH species to give water, instead of hydrogen peroxide Higher electron density on the catalyst surface triggered reaction kinetics.

[00103] Various structural models were simulated where different ORR intermediates were adsorbed on Pd, and Pt sites present on (111) facet of Pd2Ge and Pto.2Pd1.sGe. Such models are shown in Figure 10(a-d). In Figure l l(a-f) depicts structural models of OH* adsorbed on different active sites before and after relaxation. It was observed that OH* was adsorbed in bridged mode on Pd site and Pd-0 bond was longer than in Figure I lf which was due to an increase in Pd-Pd bond distance after substitution. The energy for adsorption for ORR species like OH* and OOH* was calculated using the equation: E _a ds = E _s iab+s _P ecies - E _s iab -E _spe cies. After adsorbing the species OH* on Pd and Pt atoms for both the catalysts, the PDOS for O 2p orbitals is simulated, as shown in Figure 9b. The 2p orbital electrons were closer to the Fermi level for those OH* which were bound to Pd or Pt atoms of Pto.2Pd1.sGe than on pristine Pd2Ge. The more the 2p orbital electrons close to the Fermi level, the more the tendency for the electron cloud to attract a proton forming water and then desorb from the catalyst surface. Electron density on O atom of OH* species was higher in Pt substituted species than the pristine because of the decreased oxidation state of Pd in Pto.2Pd1.sGe for charge transfer from Pt to Pd atoms. The metal M-0 (M = Pd, Pt) bond distance increased due to doping of large-sized Pt atoms, which indicated weaker M-0 bond got rid of the OH species and protected the surface from OH-poisoning and gave a highly stable catalyst.

Example 6

Comparative data on catalysts for ORR

[00104] Table 2 provides comparative data on ORR kinetics for using various catalysts. From the comparative analysis, it can be understood that the catalyst of the present disclosure has higher stability, stable upto 50000ADT cycles with comparable mass activity and half-wave potential. The catalyst of the present disclosure also provides a current density in a range of 5.7 to 6.0 mA/cm ² with minimum hydrogen peroxide and maximum water.

Table 2 Advantages of the present disclosure:

[00105] The present disclosure discloses a Pd based catalyst for the oxygen reduction reaction. The catalyst of Formula I Pt _x Pd2- _x Ge having 0.1<x<0.6. The catalyst was found to be stable up to 50000 ADT cycles and produced a current density of 5.7 to 6.0 mA/cm ² with mass activity in a range of 300 to 350 mA/mgpt. The catalyst exhibits half-wave potential in a range of 0.4 to 1.0 V. The catalyst acts as cathodic catalyst in the ORR mechanism. Pt substituted Pd2Ge catalyst exhibited enhanced performance over Pd2Ge without any Pt substitution. The present disclosure also provides a catalyst ink and electrode comprising the catalyst of Formula I. The catalyst of the present disclosure can be used in ORR both in alkaline and in acidic media. ORR using the catalyst of the present disclosure resulted in minimum amount of hydrogen peroxide and maximum water production thereby resulting in increased current density. ORR using the catalyst of the present disclosure is unaffected even in methanol crossover conditions and thus provided improved stability over other catalysts. The catalyst of the present disclosure is prepared by a simple process and is a potential candidate in the energy sector due its enhanced performance in terms of activity and stability.