This invention was made with government support under Contract Number DE- IA0000018 awarded by the U.S. Department of Energy. The government has certain rights in the invention.

[01] Introduction

[02] Hydrogen peroxide (¾(¾) is commonly used chemical for domestic and industrial applications such as disinfection, water, and wastewater treatment. Currently, ¾(¾ is produced industrially by an anthraquinone process (Campos -Martin et al., 2006). This traditional process is energy intensive and economically feasible at industrial scale owing to low yields of ¾(¾ where additional steps are required to make it more concentrated. Recently, Xia et al. (Science, 11 Oct 2019, 366 (6462); 226-231) proposed a novel method using a solid electrolyte, atmospheric oxygen, pure deionized water, and hydrogen gas to generate highly concentrated H2O2 in water, reportedly achieving 20% (on a w/w basis). This method is promising for achieving concentrated H2O2 in decentralized locations addressing the limitations of the anthraquinone process.

[03] However, this prior method may be infeasible or impractical in remote low-income communities or developing countries where access to hydrogen gas and high quality DI water is challenging or nonexistent. Overcoming the limitations of prior systems, and building on our own experimental systems, we describe a novel approach to synthesize H2O2 for onsite use without the supply of hydrogen gas and DI water, that is practical even in remote locations with supply chain limitations.

[04] Summary of the Invention

[05] The invention provides methods, composition, and systems for on-site decentralized production of ¾(¾ with atmospheric 02, water, and electricity.

[06] In an aspect the invention provides a system for H2O2 on-site production without ¾ gas or deionized water, comprising an air humidifier, a condenser, and a reactor, wherein (a) the air humidifier is configured to produce and feed a stream of air saturated with water vapor into the reactor through the condenser, (b) the condenser is configured to cool the air from the humidifier, and convert some of the water vapor to liquid form as it enters the reactor, and (c) the reactor comprises a porous solid electrolyte (ion exchange resins), proton exchange membrane, mixed metal oxide anode and a gas diffusion cathode. The solid electrolyte comprises two packed beds of ion exchange resin beads. One bed is sandwiched between a mixed-metal-oxide (MMO) anode and cation- exchange membrane (such as a proton exchange membrane, trade name Nafion), and the second packed bed is between the cation-exchange membrane and a gas (air) diffusion cathode.

[07] The arrangement is schematically described in Figure 1. A cold dilute solution of acid in water is continuously pumped through the bed between the MMO anode and the cation- exchange membrane. Water vapor that is passed through the second bed between the cation- exchange membrane and the air-diffusion cathode, condenses into liquid water upon giving up its heat through the cation-exchange membrane to the chilled acid bed. An external DC voltage (of about 4.3 volts) is applied across the electrode. In our experiments this developed a current of 0.99 Amps, for electrodes of area about 100 sq. cm. each. Upon applying this external voltage, water is oxidized to O ₂ on the MMO anode, and atmospheric oxygen entering through the gas- diffusion-cathode is reduced to H ₂ O ₂ in the presence of water inside the pores surrounding the ion exchange beds or in the presence of water film on the ion exchange beads. Freshly formed H ₂ O ₂ inside the pores of the solid electrolyte is flushed out of the reactor with the unreacted water to form H ₂ O ₂ solution and collected at the outlet as shown in Fig. 1.

[08] In embodiments:

[09] the cooling function is separated from the H ₂ O ₂ production function, wherein liquid water is first obtained through chilling a humid stream, and then separately, some of that water and atmospheric oxygen are electrically converted into H ₂ O ₂ , see, e.g. Fig. 3, optionally, wherein a stream of air saturated with water vapor is passed through an electrical chiller and the resulting water condensate is continuously fed into the delivery chamber of a nebulizer, wherein the exit nozzle of the nebulizer is aimed at the exterior surface of the air-cathode, wherein a fine mist of condensate water collects on the active surface of the air cathode, and reacts with atmospheric O ₂ in the presence of electricity to produce H ₂ O ₂ in-situ, which then drips down the surface of the air cathode to be collected;

[10] the system is configured wherein the entire reaction of oxygen reduction to H ₂ O ₂ formation takes place at the interface of air diffusion cathode, condensed water, and ion exchange beads. As the condensed water flows through the porous solid electrolyte, H ₂ O ₂ is collected from the interface (air diffusion cathode, water, and solid electrolyte) and flushed out along with residual condensed water to form H ₂ O ₂ solution.

[11] the system is configured wherein the entire reaction takes place on the water- film on the solid electrolyte beads, as air saturated with water-vapor flows through the porous electrolyte, H ₂ O ₂ is generated in the water film on the electrolyte beads is flushed out as vapor with rest of the airflow, and at the exit of the reactor, a condenser captures vapor of water and H ₂ O ₂ and coverts into H ₂ O ₂ solution.

[12] the system is configured with the use of a cation exchange membrane positioned between anode and cathode to allow the transport of protons to the cathode, and block the transport of peroxide anion ( HCF ) from the electrolyte to the anode, improving the production rate of ¾(¾ from the device;

[13] the system is configured with the use of an anion exchange membrane positioned between anode and cathode to allow the transport of peroxide anion (HCF ) from the cathode into the bulk solid electrolyte which will be flushed out along with condensed water.

[14] the system is configured with the use of a cation exchange membrane positioned in front of the anode, and an anion-exchange-membrane in front of the cathode, the anion exchange membrane prevents the transport of protons to the cathode, and the cation exchange membrane blocks the transport of HO2 from the electrolyte to the anode, improving the production rate of H2O2 from the device;

[lf|] the system is configured along with an iron based electrochemical system (Fe-EC) used for arsenic and other contaminants removal. Wherein Fe-EC system, the cathodic reaction leads to the generation of ¾ gas on the cathode, which is normally released to the atmosphere. In Fe- EC processes aeration is required to maintain dissolved oxygen levels in the water releasing humid air into the headspace of the reactor. The humid air from the head space of Fe-EC reactors saturated with water vapor and ¾ gas is supplied through a condenser to the solid electrolyte based electrochemical system for H2O2 generation described above. The ¾ gas is oxidized at the MMO anode first instead of water oxidation to oxygen, generating H2O2 at lower cell potential compared to the reactor configurations described in Fig. 1. The in-situ generated FFCFin this system may be used in Fe-EC system as an external oxidant to remove arsenic and other contaminants at large treatment volumes at low operating costs, thus avoiding the supply chain of H2O2;

[16] the system comprises inlet water, the air humidifier is configured to receive the inlet water to produce the stream of air saturated with water vapor, the inlet (input) water is of a poor quality water source, including unprocessed, untreated (e.g. without water purification treatments such as filtration, sedimentation, precipitation, disinfection and coagulation, etc) water sources, including raw pond, well or river water, rainwater or runoff, reclaimed municipal, agricultural or industrial water sources, etc. and/or

[17] the system is configured to provide an observed Faradaic efficiency of H2O2 of 10-30%.

[18] In an aspect the invention provides a method of on-site production of H2O2 with only electricity and poor-quality water, and without ¾ gas or deionized water, the method comprising deploying a disclosed system;

[19] In an aspect the invention provides a method of H2O2 on-site production with electricity and poor quality water, and without ¾ gas or deionized water, the method comprising: (a) producing air saturated with water vapor with an air humidifier; (b) feeding a stream of the air saturated with water vapor though a condenser into an ¾(¾ production reactor comprising a porous solid electrolyte (a packed bed of ion exchange resin beads) sandwiched between a mixed-metal-oxide (MMO) anode and a gas diffusion cathode, wherein the condenser cools the air and converts some of the water vapor to liquid form as it enters the porous solid electrolyte; (c) applying a DC current between the electrodes, wherein water is oxidized to O2 on the MMO anode, and atmospheric oxygen entering through the air-diffusion-cathode is reduced to H2O2 in the presence of water and this H2O2 is flushed out of the reactor with the unreacted water as a H2O2 solution; and (d) collecting at the outlet of the reactor, drops of H2O2 solution, which can be used (i) in water treatment applications such as iron electrocoagulation process used for removing arsenic and other contaminants at high throughput volumes (ii) in an UV assisted advanced oxidation processes in wastewater treatment for removing emerging contaminants of concern (iii) to make dilute disinfectant for domestic uses or in hospitals.

[20] The invention encompasses all combinations of the particular embodiments recited herein, as if each combination had been laboriously recited.

[21] Brief Description of the Drawings

[22] Fig. 1. Schematic of the configuration 1 reactor design

[23] Fig. 2. Schematic of working prototype of the reactor device. Operating current density and voltage in this experimental setup was 15 mA/cm2 and 4.23 V. The observed Faradaic efficiency of H2O2 was 10 % in preliminary experiments, and optimized in subsequent experiments to 10-30%.

[24] Fig. 3. Schematic of the reactor device wherein the cooling function is separated from the H2O2 production function, wherein liquid water is first obtained through chilling a humid stream, and then separately, some of that water and atmospheric oxygen are electrically converted into H2O2

[25] Description of Particular Embodiments of the Invention

[26] Unless contraindicated or noted otherwise, in these descriptions and throughout this specification, the terms “a” and “an” mean one or more, the term “or” means and/or. The examples and embodiments described herein are for illustrative purposes only and that various modifications or changes in light thereof will be suggested to persons skilled in the art and are to be included within the spirit and purview of this application and scope of the appended claims. All publications, patents, and patent applications cited herein, including citations therein, are hereby incorporated by reference in their entirety for all purposes. [27] This invention provides for on-site decentralized production of lUCUwith atmospheric O2, poor quality water (e.g., pond water), and electricity. It overcomes the supply chain limitations of more stringent inputs demanded by current state of the art devices for ¾(¾ production.

[28] In our novel approach, we use water vapor in a stream of saturated air to obtain a ¾(¾ solution. A fraction of the water molecules are converted to ¾(¾ and the rest of condensed water is used to capture and flush the ¾(¾ into an outlet stream. Our H2O2 production reactor comprises a porous solid electrolyte (a packed bed of ion exchange resin beads) sandwiched between a mixed-metal-oxide (MMO) anode and a gas diffusion cathode. A commercially available air-humidifier feeds a stream of air, saturated with water- vapor, that enters our reactor through a condenser. The condenser cools the air and converts some of the water vapor to liquid form as it enters the porous solid electrolyte. Upon applying a DC current between the electrodes, some of the condensed water is oxidized to O2 on the MMO anode, and the atmospheric oxygen entering through the air-diffusion-cathode is reduced to H2O2 in presence of water at the solid electrolyte and air cathode interface. This H2O2 is flushed out of the reactor with the unreacted water as a H2O2 solution. At outlet, drops of H2O2 solution will be collected, which can be used (i) in water treatment applications such as iron electrocoagulation process used for removing arsenic and other contaminants at high throughput volumes (ii) in UV assisted advanced oxidation processes in wastewater treatment for removing emerging contaminants of concern (iii) to make dilute disinfectant for domestic uses or in hospitals.

[29] One embodiment of this invention is as follows. A bench scale electrochemical reactor was built with rectangular polycarbonate sheets (14 cm x 14 cm) to form two closed chambers (Anodic and Cathodic) separated by an ion-exchange membrane (e.g., Nafion, CMI-7000 from Membranes International Inc. or any other cation-exchange membrane). The anode chamber has an empty volume -100 ml, and is filled with cation exchange resin beads (e.g., “Amberlite IRC- 120H” obtained from thermo scientific) as a solid electrolyte. One side of the anode chamber is formed with an MMO mesh (mixed metal oxide IrC RuCU coating on Titanium mesh, 8 cm X 8 cm from Magneto Special Anodes, Netherlands), and the other opposite side of the anode chamber is an (8 cm X 8 cm) cation exchange membrane. This MMO anode is in close physical and electrical contact with cation exchange resin beads located inside the anode chamber. The cation exchange membrane too is in close physical and electrical contact with the cation exchange resin beads. A dilute chilled solution of sulphuric acid (10 miliMolar) is continuously recirculated through the cation exchange resin bed, at a flow rate of 10 mL/min with a peristaltic pump. The dilute solution of sulphuric acid is maintained at a chilled temperature (about 5 C) by passing the tubing through an ice bath. The cathode chamber has an empty volume -100 ml, and is also filled with cation exchange resin beads (e.g., Amberlite IRC-120H) which acts as a solid electrolyte. The other active surface of the cathode chamber is an air diffusion cathode (8 cm X 8 cm, recipe was described in Barazesh et al 2015). The cathode chamber has a multiplicity of air-inlets at the top side, and a multiplicity of outlets at the bottom side. The outlets at the bottom side are connected to a collection chamber that is evacuated continuously with a small air pump (1/16th HP). The inlets at the top side are supplied with air saturated with water vapor at about room temperature, obtained from an evaporative humidifier (e.g., a commercially available model Vicks Warm Mist Humidifier, V745A/V745-JUV). The air saturated with water vapor from the evaporative humidifier is sucked into the cathode chamber owing to the depressurized collection chamber connected to the cathode chamber. During its passage through the interstitial spaces in the cathode exchange resins, the air experiences a drop in temperature owing to the passage of chilled sulphuric acid on the other side of the cathodic ion exchange membrane. This causes a release of pure water (¾0) in the interstitial spaces in the resin bed. Chemical reactions described above are driven by passage of externally supplied electricity to the device. In this embodiment, a DC voltage of 8 Volts was applied across the MMO anode and the air-cathode, and a current of 2.5 Amps was observed. The condensate captured in the collection chamber under these conditions was about 100 mL per hour, and it was observed to have an ¾(¾ concentration of 1600 mg/L. (measurement made using a HACH DR 6000 spectrophotometer with the titanium(IV) sulfate method at 405 nm). We observed that this production rate and this H2O2 concentration could be maintained for several hours without degradation of the production.

[30] In another embodiment, a plurality of heat extraction devices (e.g., solid-state Peltier cooling modules (12V 6A Thermoelectric Peltier, Eujgoov, purchased from Amazon.com, or cooling coils from a small vapor compression chiller, e.g., Frigidaire chiller model EFMIS137) are installed in thermal contact with (but electrical isolation from) the MMO Anode. Operation of the cooling mechanism leads to continuous heat extraction from the anode chamber, and therefore also from the cathode chamber. The interstitial spaces in the resin beads in the anode chamber are filled with diluted inactive acid (e.g. 10 mM dilute sulfuric acid) to improve conductivity of the ion bed. Air saturated with water vapor is passed through the cathode chamber as described above. Pure water condenses at the surfaces of the ion exchange beads in the cathode chamber as described above, passage of electricity converts some of that water into H2O2 as described above. Condensed water, generated ¾(¾, and supplied air all exit together into the low-pressure collection chamber, from which the air is extracted continuously with a small pump as described above.

[31] In another embodiment of the invention, the reactor is designed and filled with cation exchange resin beads as described above, with differences: (1) the resin bed in the anode chamber is filled with a dilute (10 mM) solution of sulphuric acid, but it is not circulated, and there is no cooling of the anode chamber; (2) the catalyst side (of carbon black) of the air cathode is made to face away from the resin bed; and/or (3) there is a collection mechanism for the H2O2 formed on the exterior surface of the air-cathode, as it drips down into a gutter. In this embodiment, the cooling function is separated from the ¾(¾ production function, compared to the first two embodiments described above. A stream of air saturated with water vapor is passed through a small electrical chiller (such as Frigidaire chiller model EFMIS137) and the resulting water condensate is continuously fed into the delivery chamber of a small electric nebulizer (e.g., “just Nebulizers” model J- 1100312). The exit nozzle of the nebulizer is aimed at the exterior surface of the air-cathode. Fine mist of condensate water collects on the active surface of the air cathode, and reacts with atmospheric 02 in the presence of electricity to produce H2O2 in- situ, which then drips down the surface of the air cathode to be collected and used.

[32] With this invention, there is no need for H2 gas or deionized pure water to produce H2O2 solution. All needed supplies are widely available: namely atmospheric oxygen, any acceptable water for the humidifier, and some electricity, thus overcoming the supply chain limitations of the H2O2 production of prior methods.

[33] Advantages of our novel approach include:

[34] (i) on site generation of H2O2 using locally available resources with minimal supply chain;

[35] (ii) does not involve hazardous hydrogen gas;

[36] (iii) continuous recirculation of the chilled dilute acid through the anode chamber reduces the ohmic heating of the constituents inside the reactors (e.g., electrolyte, ion exchange resins and membrane) especially at high current densities ranging from 5 mA/cm2 to 1000 mA/cm2;

[37] (iv) locally available water can be used to make water vapor which will be fed into our reactor;

[38] (v) regions where high humidity exists, air can be pumped directly into our reactor to make H2O2. These conditions can exist near coastal areas, and locally within centralized plants for water and wastewater treatment;

[39] (vi) our process does not require expensive and highly flammable hydrogen gas as an input supply and therefore is safer and less costly than prior H2O2 production methods such as Xia (2019, supra);

[40] (vii) practical applications including community and municipal scale drinking water treatments, community and municipal scale recycling and reuse of wastewater treated effluent, industrial wastewater treatment, treating hospital wastewater.