I BACKOMOUKB OF H VE T!O

A. ield of the Invgft foa The present .kveatkm elates ge&eml!y to the i¾id of vapoor hase wae electrolysis, mi in particular, to an mprovemen thereof by engaging such, with photovoltaic (FV) sterns m& imegra iug the mal aad wa e mana ement imo said system.,

B _* Description of the Related Art The prmte oft of one of the simples moleetites _* hydrogen from water and. sunlight Is an attractive option for storing renewable energy. Proton exch nge meaibraae (REM) electrolysis is an already commercialized conce for hydrogen generation, with proven cost eileetive capabilities in various industrial applicati ns such as cooling power plant ti« m? generators, semicotKluctor processing and olmmai gra n , among others, However, ibr the specific application of hydrogen for en r generation, the cost as to decrease farther. The cost, breakdo wn of a 3 cell tocks system. %vitb the corresponding ower sup ly baatfcs resulting » a production equal to Bkg da reveals the major contribution of the eel! slacks on the capital cost More precisely, 53% of cost is attributed to the cell stack, from which the Sow fields and separators have the major eontrfbrnion. ⁵ Moreover, the- wet systems for which liquid water is needed for their operation will be a hurdle in regions with limited water su ply. Any compotitiori with the agriculture sect r _* where water scarcity has great relevance, should he avoided. Theref re, ther is a need in the art to provide an efficient wa for generating hydrogen with water from ambien air humidity as reagen and light as energy sonree, Alkaline electrolysis is the most m t re technology today and there are a few drawbaeks which make thei oneration. difficult, They operate m concentrated alkalirse electrolyte (5-10 Κ.0Β} which directly p ses stringen t material property requlreMenis for encap i n of the device, Additionally, these high concentrated electrolytes are able to absorb COz from the ahrjospnere to form Insoluble species sueh as ¾(X¾ which precipitate inside the device and ock the porous electrodes, leading to reduced peri¾rntance. Moreover, alkaline eleetrolysers work at hi h current densities which lead to bubble formation on the electrode surfaces _*

I To prevent cross-over o p oducts, pressure a anod and sathodfe

at all times, &kt* Is mt the case for Obese systems. Tills m k s their operation (start-up aid shut-down) flexible.

The water ieed i^qat ements arc also ry stringent To avoid fouling of the mm mm extra pure water with low ionic concentrations is needed. ΊΜ& requires additional energy., making the deviee less energy efSeieni

Present uweatkm solves these above mentioned problems* it provides m assembly of a FY module and a two compartmen e ectmlysis apparatus which is mad using low cost methods nd devices. The ap aratus uses water prese t in. outside air as a reagent for hydrogen production _* The ehe&dian shifts of outdoors abiotic conditions subjects the p aratus of present invention t v r ous cond ti n . Present invention solves that problem. For keeping a satisfactory' level of hydration while m i t inin a device operation at sul cient temperatures, this invention provides a well-designed tcnujerature arid hydration management sy em¾ir teg . During the day, sunlight is heatiog up a heat absorber/collector directly connected t a reve s ble water sorption material, thereby mdudasg water release from said material to cathode compartment and dir¾sk n of water through the ion excluinge material., thereby wetting it Water is xidiml ^uced at the aaode/e^thrKie and l¾ is collected while C¾ is released into air, While m operation doting tire night, eool h mid air circulates through the device and the reversible water sorption material replenishes. Such device reaches a solas- to hydrogen efficiency above 5%.

1 . SUMMARY OF THE I VENTION

The present invention solves the problems of the related art by a water splittin apparatus.. comprising 1} a radiation absorbing material {T r heat absorber/collector lement especially designed for efficient absorbing light energy and for releasing it as heat), 2} a reve sibie water sorption material (tor Instance element that comprises a materia! especially designed fmm. absorbing water vapour from ambient air and releasin it when heated) whereby the reversible water sorption material is connected with the mdiation absorbing material !or heat exchange, 3) a re ac i n reaction gas unit at one she connected for water va onr exchange with a permeable element to the reversible water sorption material and at anothe side connected with a porous cathode t an ion exchange mate ial to allow water v¾n nr and ions to pass and 4} a water oxidation reaction gas unit■ ^■ connected at another side with a porous anode to the ion exchange materiai so that the ion exchange material is intermediate between cathode and anode.

In yet another embodiment the inventions solves the problems f the related art by an electro- reaction apparatus, comprising I ) a radiation absorbing material (for instance such heat absorber/collector element especially designed for efficient absorbing light energy and fo releasing it as heat ,:!) a reversible water sor tion mat that comprises a. material especially designed from absorbing water vapour from ambient air and releasing it when heated) whereby the reversible water sorption material is contacting the radiation absorbing material for heat exchange, 3) a reduction reaction gas imit at one site contacting fo water vapour exchange with a permeable element to the: reversible water sorption material and at another ' Side contacting with a porous cathode to an ion exchange material to allow water vapour and ion exchange and 4) a water oxidation reaction gas unit contacting at another side with a porous anode to the ion exchange material and further characterised in that reduction reaction gas unit comprises the reversible water sorption material for instance as a _: wall or the reduction reaction gas iiiiit shares a permeable enclosing element wim said the lm'ersibie water sorption material and whereby the water oxidation reaction gas unit at least one Inlet fo ambient air so that when the absorbin element s radiated the reversible water sorption material releases water vapour into the reduction reaction gas unit and when not radiated the reversible water sorption material absorbs water front a hydrated vapour atmosphere.

In accordance with the purpose of the invention, as embodied and broadly described herein, the invention is broadly diawn to a water splitting apparatus, coMprising 1) a radiation absorbirig material Ifor instance sue^ designed for efficient absorbing light energy and for releasing it as heat), 2) a reversible water sorption material whereby the reversible water sorption material is connect with the radiation absorbing material for heat exchange, 3) a reduction reaction; gas; unit at one site connected for water vapour exchange with a permeable element to the reversible water sorption material and at another side eo ecied with a porous cathode to an ion exchange material, to allow water and ions to ass and 4) a water oxidation reaction gas unit connected at another side with a porous anode to the ion exchange material so that the ion exchange material is intermediate between cathode and anode or to an eleetro-reaetion apparatus, coinprising 1) a radiatio absorbing material, 2) a reversible water sorption material whereby the reversible water sorption materiai h contacting theaalaiiors absorbing mteil for beat exchange, 3} a red«ctioti rection gas anil on site mataetieg tor water vapour exchange with a c element to the te rsbk wate sorption material and at another side contacting wife a porous cathode aa km exchange material to allow water vapour and ions to pass and 4} mm oxidation w im as unit eatatiig at another sie with a porous d% to the im exchange material and t¾rther eha^tetisod i» ifcare ueii ft reaction gas unit lmes a f*emieah!e eadosisg element ¾¾ said f¾e water sorption material and the water oxidation eaction gas unit at feast one inlet tor ambient air so that whe the absorbing element Is radiated the revmibfc water sorption material njeases water vaponr into the reduction reaction as ttnit and when not radiated the reversible water sorption material absorbs waster f m m $q vapour atmosphere, hi one aspect of the invention, sneh apratu here above described is eharaefefi.«e<! m that the reduction reaction gas anit shares a vapour pemieabie eiielosing element with said a ersihle water sorption material

Another pamealar em oi!imeiit of the invention is that the gas unit is a chamber, c ker or enclosure. In yet iother embodiment the ion exchange material is an alkaline membrane. Optimal function s obtained when the wter oxidation rection gas unit is adsfde to tuetion a convection gas conduit because it is elongated container or enclosure wih at least one aeriwe at one extended skle and with at least on aperture at another extend side of said water oxidation reaction gas unit container.

The reversible water sorption material comprises material especially designed for a oring water from ambient air and releasing it when heated. Suitable materials for uch functi n are any of the following: a hygroscopic substance,, a hydrohllie material, a hydrotiilie powder, a porous hydrophibe material, a niesoporo hydwpbilie material, a microporous bydrop lie m eri! or a mixed mlororxrou / letox>rous hydrophl!ie material.

The radiation absor bing mater ial especial by designed to absorb radiation comprises one of the materials of the grup consisting of black fused silica, materials havin increasing inchi g points, heat-resistant metal, heat resistant pol ymer comprising f &w iron and glass comprising ferrous Iron, The sao e and cathode are electrically connected with a source of eeen city whereby in me mfeodimeni of present Invention of en agin the electro-reactor apparatus with photovoltaic (FY) system this d ct z l i» that the radiation shsorhkg mater l contacts or is connected with m array of eeleeiieally connected space separated solar cells encapsulated in a glass md a light transparent insulator so that light irradiates the solar cells and the radiation absorbing material. Such solar ceils or arrays of solar cells are electrically connected to anode aid cathode.

The above described invention has particular advantages thai by usin Ion exchange materials (for instance a polymer ion exchang materials (PBM) and ah as a water source, the need of using KOH is limi ated so thai device degradation due to corrosive materials is eliminated Device degradation due to the use of corrosive liquid concentrated electrolytes uch as KOH is a problem in the art Another particular advantage of the present nveated pp ratus is that nly low or no impurity levels are maintaine in the a atus, By using Ion exchange materials (for instance a polymer ion exchange materials (PEM) and air as a -water source, the need of using KOE is eliminated. In the ar there is a decrease i» performance due to the reaction of KOH with C02 in air to make carbonates such as f a€<¾ (insoluble).

Y et another particular advantage of present Is that no increased pressure is req uired on either sides of the apparatus (in either of the as reactio units). Using air as a feedstock mere is no need for operation at high pressures as FHM electrolysis. In fee art pressure increase on either side of the membrane results In difficulty in start-up and shu do n.

The apparatus of present invention has no bnhhle formation. The absence of liquid water eliminates this problem. Bubble formation in liquid electrolysers at high current densities <> I Vcttf ) is a problem in the art, The apparatus of present Invention can be made as a lightweight and low cost device since by its use of air the fe dstock for water electrolysis, the need of pipes tor water supply is eliminated The devices of the art. are heavy and expensive devices due to the use of water piping and compressors system. The apparatus o reseat invention hm so or onl limited lsiomii at the memfemse. By sing air as the feedstock for water electrol sis* t e need of high purity water is eliminated. The dev ces of the ar ne d high purity water and water purifes in order to av id poisoning of t e membrane.

In the art for vapour phase electrolysis, tmder a conveeied flow with 100% |¾ a limited camsa density (40 mA/am ³ } is reached dne to mass transport problems, The apparatus of present Invention allows to use such high c »t densities _» evsa when the ambient Rll Is lower than 1( 0%, due to incorporation of water adsorbing materials which ensure enough ater sapply. The apparatus of present invention allows higher activity and therefore higher efftcierseies achieved. For instance when operational the reversible water adsorption material releases water y nhanced tempemtore du to absorption f light therefore keepmg the relati e humidity (IIH) high. By the desi n, of present invention gh relative humidity is achieved u to RH 1 t 4

The apparatus of present invention prevents damage 4m to water frost, by resor tion of water vapour by the reversible water sorption material during the night cycle and du to adsorption heat generated by the reversibl water sorption materia!. Frost is a problem, in the art of solar* driven hydrogen, producing units. ³

Farther of the present invention will become apparent from the detailed desenption give hereinaifer. However, It should be understood that the detailed description and specific examples while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope o the invention will become apparent to those skilled in the art frot this detailed description. It is to ho understood that both the foregxhn general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention* as elauned, S me embodi.me¾ts of ^' the invention, are set forth directly below;

fmoti, Invention concerns an apparatus or a member of an electro-reaction apparatus comprising I) a radiation absorbing material or component comprising such snateriai (4), 2) a reversible water sorption material or component e& dsin such b material■($ _» whereby the reversible water sorption material or eeia eaeat comprising s«eh material (§} ¼ connected with or oMttcts a radki ii absorbing material or component comprising sacfc material (4) for h t exchange aasd w½rehy the t¾versihle water s r tion materia! or com one t composing sancfe materia! (S) lor mter va our exchange at another mk Is cotsaec ed with, or con cts a eac ion unit w erehy t¼ rea i n m forther eonmrises a redm ion re&ctkms gas w (#) formed by a pemss cathode (?) and a water ox afKaa eacti n gas mk (10) foimed b & porous anode (9) separated by an ion exchange material or eoniponent co p isin sueh M ter al (!$} to allow wate and io to pass.

In a a ticular embodiment In this apparatus or apparatus element the reversible ate sorption material or com n nt comprising such m terial (S) is at the other side co peted with the o ous cathocte (?) so the that reversibl water sorption material or component comprising such nmterial (5) forms the reduction reaction gas nnii 6) and w¾ereb the porous cath e (?) is in turn being connected with or contacting the ion exchange material or component comprising such material <S) to allow water and ions t pass and at the other side of the ion exchange .material or component comprising such material (§}, a water oxidation reaction gas unit (10) is connected with or contacts a porous anode (f ) so tlmt the ion exchange material or component comprising such .material (8) is Intermediate h ^ee cathode (7) and anode (9),

in yet another particular embodiment in this ar us or apparatus element, the reversible wate sorption nnrterial or component comprisin such material (5) m at the other side connected vith the porous anode (9) the tlmt reversi le water sorption material or component comprising such material (5) forms the oxidation reaction gaa unit (10) id whereby the porosis anode. (9 ) is in turn being cmineeted wit or contacti ng the ion exchange material or c mpo ent comprising s en material (8) to allow water ami ions to pass and at the other side of the ion exchange material or component comprising snch materia! {$% a water reduction reaction gas uni (6) is connected with or contacts poroiss cathode (7) so that the ion exchange material or eomporseni comprising such material <$) is intern^diate between anode ($> and cathode {?}, in yet another partienfar embodiment in this apparatus or apparatus element the reversihie water sorption material or so poaen c rising such material (5) is at the other side connected with the porous cathode (?) so the tha reversible water sorption material or component comprising such material (S) forms the reduction reaction ps

the ion exchange material or component comprising snch material (8) that at the other side is connected with or contacts r porous anode (9) so that the ion exchange material or component comprisin such material (8) is intermediate between cathode (7) and anode (9) to allow water and ions to pass through the ion exchange material or component comprising such material (8), and whereby porous cathode ffi forms the water oxi dation reaction gas unit (10).

la yet another particular embodiment in this apparatus or apparatus element comprises I) a radiation absorbing material or component comprising such material (4;), 2) a reversible water sorption material or component comprising such material (5) whereby the reversible water sorption material or component comprising such material (5) is connected with the radiation absorbing

(4) for heat exchange, 3.) a reduction reaction gas . umt {€) at one

water vapour exchange with the reversible water sorption material or component composi g such material (5) and at other side co ected w (¾ in rum connected with an io exchange material or component com risi such material (8) to al low water and ions to pass and 4) at . ^" the other side of the ion exchange niaterial or component cohiprising $uch material (8), a water oxidation reaction gas unit (10) connected with a porous anode (9 so that the ion exchange material or component (xmiprising such material (8) is intermediate between cathode (7) and anode

The apparatus or appar atus element of present invention "can ^' be characterised n that the water oxidation reaction gas unit (10) is connected for water vapour exchange with the reversible water sorption material or component comprising such material S) and at another side connected With a porous anode (9), m turn connected with an io exchange material or component comprising such materM

the other side wf he ion exchange material or component comprising such material (8), a reduction reaction gas unit (6) connected with a porous cathode (7) so that the io exehaage material or component comprising such material (8) is intermediate between, anode and cathode.

In yet another particular embodiment this apparatus or apparatus element of present invention is etoracteris i that the radiation absorbing material or component comprising such material (4) which radiation absorbin material or component eomprisisg s¾c¾ material (4) lays on t e revers ble wa er sorption .material or compo ent comprising such material (5), the re ersible water sorption ma eria or component eonujsising ueb ir eriai (5) tor rig a of the t«d«eti reac i n gas taut whereby the induction reaction gas timt (ύ) comprises the a porous cathode (7) as wall , i he e and i e e^i te km exchange material or component com rising such mater d (8) se ara es the poross cathode (?) d p ro s Mode (9) and whereby the rous saode (§) forms a wall with the water oxidation reaction gas unit (18). The above described apparatus elements can be connected with an array of electricall eoaiiected s ace separated solar ceils ncapsul ted I» a light transparent insulator lays on the radiation absorbing material or c#mjpeneii comprising such nui erlaJ (4) which .radiation absorbing material or com onent comprising sneh material (4) lays on the reversible water sor tion material or expo e coa irismg such nuuerial (S). Furthermore this can be in a particular embodiment be characterised in that the water oxidation reaction gas unit (18) comprises at least one inlet for ambient air so that when tbe radiation absorbing material or component comprising such material (4) is radiated the reversible water sorption material or component comprising sueb material ( ) releases water vapour into the redactio reaction gas unit ( ) arid when mi radiated the reversible water sorption material or com onent comprising msh material (5) absorbs water from an aqueous vapour atmosphere,

in general tbe water to pass the ion exchange material or component comprising such material is water vapour.

Particular adaptations on tbe apparatus or apparatus element of presen in vention cm e as follows; tbe reaction unit is a chamber, container or enclosure; tbe gas unit ( _t 1#) is a chamber, eomainer or enclosure; the ion exchange material or expo e t comprising such material (8) Is an anion exchange material or com onent comprisin such material; ion exchange material or com onent comprising mch material } is an cation exchange material or component comprising sueh material; the water oxidation reaction gas unit (18) is adapted to nctlon as a convection gas conduit because it Is an elongated container or enclosure with at least one aperture at one extended side and with at least one aperture at another extended side of said water oxidation reaction gas unit (18) container; the water oxidation reaction gas unit (18) and the reduction gas unit have to po sibility to be sealed; the reduction gas unit (6) comprises a vent which comprises sel&opetaag sad self -dosing c os«xe _» for i»sta»ee a seli½pe»k or selfk;iosir¾g id, shutter or cover far opening or closing sa d vent

In a parne dar regulator or actuator tMictionally eormeeted to the cl sure. This regulator or actuator can he ro r mme to open the closure ibr water ds tion by the reversible water so tion materia or component comprising sueb -material {$} or close he ekmrrc to preventin dehydration of the reversible water s r i n material or component comprising such materia! (5) d ne^ing on the hiunidlt in the am ient air surmunding said apparatus. Thi regulator or actuator can be tsmmsd to open the cl su e during the night for water adsorption by the reversible water sorption material or component, comprising such material (§> sad to close the closure during the day thereby preventing dehydratioii of d e -t&tmM® wate sor tion material or component comprising such material ($}. Furtb^rrnore in a partieular emfx?d¾?e¾t the apparatus further comprising a humidity smmt Emotionally and or a light seasor comtectedl to said regulator or actuator.

Other specific embo iments of the ap a tus of apparatus element o present invention is sash ¾¾tereh the radiation absorbing material or composmt comprising sueti material (4) does not comprise a phase transition material.

Fanfeuiar suitable, for instance for transportatiori, is the bodiment of present invention whereby the reversible water sorption material or componen comprising suc material (5) is demountable so that it can be replaced by another reversible water sorption material or component comprising such material. (5) with the same, similar or other capabilities,

in present kwemlon the reversible water sorption materia! or continent comprising such nmteriai {$} can comprise one of the following; hygroscopic substances, hydrephiiie material, hydrephilie powder, a porous bydropM!ic material a mesoporous hydmphiiie material, a mieroporoos hydrop iiic material, a mixed rmeropor BS / microporons hydrophil!c material, a material that exhibits a reversible changing hydrophilicity in function of temperature. In present invention the reversible water sorption material or component comprising such material (5) cm also comprises one of the materials of the group eoosistfeg of copper, aluminiu _* i on, staloless steel, black fused silica, materials having increasing melting points,, heat-resistant metal, heat resistant olle comprising ferrous iro and glass comprising rerroos iron. Other embodiments of the apparatus of present invention are that he anode (9) ana cathode (7) are electrically connected with a source of electricity, that the radiation absorbing material or component comprising such material (4) contacts or is connected with an array of eclectically connected space separated solar cells encapsulated in a light transparent insulator so that light irradiates the solar cells and the radiation absorbing material or component comprising such material (4), that the radiation absorbing material or component comprising such material (4) is a heat sink, that series of solar cells or arrays of solar cells whereby series of solar cells or arrays of solar cells are electrically connected to anode (9) and cathode (7), and/or that series of solar cells or arrays of solar cells, whereby the solar cells or arrays of solar cells are comprised in an unit that is demountable from the hydrogen producing unit.

This apparatus according to any one of the previous embodiments is particular useful and can be used for oxygen and hydrogen production from ambient air.

2. DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

2.1. Definitions

The term "water splitting" means the reversible cleavage of water into its constituents, oxygen (0 ₂ ) and hydrogen (Hi). Water splitting is achieved by many different technologies of which electrolysis is an example. Water splitting by electrolysis is achieved by applying electric energy on two electrodes, termed anode and cathode. The anode is positively charged and splits water into oxygen, protons (H ⁺ ) and electrons (e ^" ). Electrons are transported through an electrical wire to the cathode. Protons are transferred to the cathode through the water which contains a salt to carry this ion current. The cathode is negatively charged and brings together electrons and protons to form molecular hydrogen gas.

The term "electro-reaction apparatus" (ERA) means an apparatus that performs any electrochemical reaction, both galvanic as well as electrolytic reactions, and includes water electrolysis reaction, carbon dioxide reduction reaction and other electrolytic reactions but also fuel cell reactions and other galvanic reactions.

The term '"porous" means any form of macro-, meso- and micro-porosity and includes pores of all shapes and dimensions. The compound for which a material is porous, can be in any physical state such as liquid, vapour or solid.

The term "radiation-absorbing element" means an element comprising a material that is specifically constructed for such a purpose, and includes material such as copper, aluminium. i n _* stai less steel or be t resistant polymer glass containing quantities of ferrous 1KM or other material selected to provide a s milar effec The term "radla an" encompasses- mdlation ac oss he electromagnetic spectrum, includin infrared, visible light and ultraviolet radia otL The term "reversible water sorption material " means an element comprising a material that is able to adsorb water from vapour phase sash s sir and Is able to relea e the adsorbed water again. Adsorption and desorpiion hap en, la different conditions such as variation in temperature or relative ktmidity. Such mentioned materials can be any type of meso- or miet oroys materials such s corhon, silica, molecular sieves, zeolites or metal organic roeworks (MOF) or a combination thereof.

in the present application, a radiation absorbing material, a reversible water sorption material or an Ion exchange material is in the meaning of respectively a radiation abs rbin material or ¾ componen conmrisirj such material, a reversible water sorption m te ial or a component comprising such m terial or an ton exch nge material or a component comprising such materia!

2 etaii«*l < i¾crtp ie«

The following de uled description of the invention refers to the accompanying drawings. The s me referenc nambers in different drawings identify the ame or similar elements. Also, the following detailed description does not limit he invention. Instead, the scope of the invention is defined hy the appended claims and equi alents thereof,

Se eral documents are cited throughout the test of Ms specification. Each of the docum nts herein (loeludmg a&y manufactu ers sp^iik-atloos, instructions etc.) are hereby Incorporated by re erence; however, there is no admission that any document cited is indeed prior art of the present Invention.

The present invention will be described with respect to particular emboilinicnts and with reference to certain drawings kit the iiwention is not limited thereto kit only by the cini s. The drawings described are only schematic and are non-limiting, In the drawings, the shse of same of the elements may be exaggerated and not drawn to scale for illustrative purposes. The dmiensions and the relative dimensions do not cortxssp nd to actual rednetions to ctice of the invention.

Furtl¾eenore _s the terms first;, second, third and the like in the description and In the claims, are used for d stinguishing between similar elements aud not necessarily for deserlhin a seq ntial or chronological, order, It is to be understood that the terms s used ar interchangeable nder appropriate circumstances aad that the embodiments of the kventioa described herein are capable of operation in other e ences than described or illus^ toesa.

Moreo er, the terms top, bottom, ewer, under aid trie like k the description am! the clai s am used for desc ip ive purp ses and not t x &dlf for describing relative positions _* It is to be mxierstood that the terms so wed are interchangeable under appropriate t½eemsta»ees ami that the $M¾odif»e¾t& of the m ntion d sc ibed herein are eapable of o ration in nmer ie atiOiB than described or Illustrated herein, It is to be noticed tha the term "compr!deai *, used in the claims, should net be interpreted as being mstricted to the means l sted thereafter; it does not exclude other elements or s e s, it is thus to be interpreted as specifying the presence of the stated features, integers, steps or om onents as referred to, but does not preclude the presence or addition of one or more other features, integers _* steps or components, or groups thereof. Thus, the scope of the expression device co ris ng means A and B" shoul «ot be limited to the d vice® c«asistk only of comr mests A and B. It means that m x res ec to the present invention, tbe only relevant components of the evice are A and B.

Reference throughout this sp dfte mn to ^w ne embodteiest" or "m. embo ktew means that a particular fea ure, stateture or characteristic described k cosmec ion with the em odimen is included m at least one eunbodimeni of the present Invention, Thus, appearances of the phrases ⁴ 1n one emb diment" or *%* an embodiment k various places throughou this speeilieadon are not necessarily all retemng to the same embodiment Furthermore, the particular l½nsres _s structures or ehai¾eteristies ma be combined k any suitable manner, as would be ap rest I» one of ordinary skill in the art from this disclosure, one or more embodiments,

Similarly it should be appreciated that In the description of exemplary embodiments of the invention, various features of th Invention are sometimes gtottped together la a single embodiment, figure, or description thereof tor the purpose of streaisiinlng the disclosure and aiding the understanding of one or more of the various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting ait intention that the claimed invention requires more features than are expressly incited k each claim. Rather, as the following claims reflect. Inventive aspects He less than ail features of a single foregoing disc lose emhodiment. Thus, the claims following the detailed escri ion are hereby expressly Incorporated Into this detailed description, with each claim s anding on its own s & se a a e embodiment of t¾« in ention.

Foilherniore, while som en^od eriis described herelo iaohsste- som but itot other features imjlud d in other em odimen , eonihinaiions of features of ifferent embodiments are meant to be within the scope of the Mvention, aad f m different embodiment * as would be un rst o by those In the a for example. I the t diowing elainis, any of he claimed em odime ts can he used hi any combination,

O ifee sustainable energy sources which am available nowadays, solar energy is tbe only source that has in theor the potential to meet at! our energy needs. Although photovoltaic technology, converting sunlight into dectrfdty* ha bees widely developed, it is ½?apahle of storing tbe produced energy; As the ceor huiion of solar energy in the total energy oduction increases, electricit network operators will eventually reach their limit to cope with the ktennittent nature of solar p&mt (day/nigh cycle, elo tds). Storing solar energy in ebemieal. kntds ©fta the desired practical compact type of energy cooversiom ie> h gh energy storage densities and ease of tfans oitation, The production of one of the simplest molecules, hydrogen (¾), from water and s i!ight is an attmetive option,

Aihaiine electrolysis is the most mature technology today. However they have a tew drawbacks which makes their operation difficult They operate in concentrated nlkaline electrolyte (5~ 10 K.OH) which directly supposes stoingeni material property requirements for encapsulation of the device. Additionally these high concentrated electi l tes arc able to absorb CO2 frora the atmosphere to form insoluble species such m ¾COs which precipitate inside the device and block the parous electrodes, leading to reduced perfnrni iee; Moreover* alkaline eieetrolysers work at high cnr ent densities which lead to bubble totmatlon on the electrode surfaces .?

Proton exchange mesnbrane (PEM) electrolysis Is an already eommereialixed concept fo hydrogen generation, with proven cost, elective capabilities in ari u industrial applications such as e«oiing power plant torbine generators, senneondnetor processing and ehron atog phy, among others. However, for the spee-iile application of hydrogen for energy generation, the cost has to ikriher decrease. The cost breakdown of a 3 cell stacks system with the corresponding power supply banks resulthig In a prodoetiort ennal to !3kg day reveals the major contribution of the cell stacks on the capital cost More precisely, 53% of cost is attributed to the cell stack, fro which the flow fields and separators have tbe major contrlbafion,* Moreover, most conc p s are ased tm wet. systems for which the seed of liquid water for their oj atio«. could be a hnrdk m regions with limited water s pply, Any competition with the agriculture sector where water scarcity has great tevm shook! be avoided.

To preven cross-over of products, pressure at anode and cathode compartment lias to be equal at all times, which s aot the case for these system . This makes their erati n (start-¾ and shutdown) less flexible,

The water feed requirement are als very stringent, To avoid fbtimg of the e*»bsa»e _s extra pure water with low ionic coocemration is needed. Thk requ res additional energy, rimk½g live device less energy efficient.

To overcome the afbreai stkned drawbacks such as costs, design and water availability, present in ion em tm a apparatus adapted not to \ % the use of highly concentrated liquids and recirculation eqni rneni as is the ease with conventional botovo!tak-eieetrriiysis (PV-E) systems. The de ig of the apparatus of present invention is based on rssing moisture contained m outside air as a water source. Water supply tnanageinent is very simple, since air s ly s achieved by natural convection. With 10% soiar~to~ ydrogen efficienc such installation mil consume wa er at a rate of ax 30 g mC ² h ^*1 to genera e m, 2 g mf ² hf * of hydrogen, or an energy equivalent of 40 kJ n ^¾ b ^'s < The m nimum needed air volume at 20 °C, 1013 hP and 611% relative humidity then Is ~2 nr h" ¹ V ² . Even is the Sahel desert, at an wm$t relative humidity of about 20% & tem erat tes of 2 °C» 0m cubic meter of air contains 6 g water. Additionally, frost protection will not be needed while avoiding to jeopardise local fresh water supplies. All these advantages of air-fed water splitting cells of the ap atus of present invention arguments for a paradigm shift for the devel ment of the specific technology.

Th air-fed PV-E devic of present invention will serve the following iknetions;

i) adsorption of water from air and absorption of photons from the sua .

It) the photogenerated current will enable the net o idafion of water to ions and oxygen, in) transport of ions through the Ion excj &nge nuderlal (IBM)

tv) Evolution of hydrogen !a the second com afta^ent i absence of air.

2 _* S _* Exam les 0» the device, deseripilo»<% e a iE>«i

It has been reported that in the presence of highl active electro catalysts, the onse potential for electrolysis oecorred at higher voltage tor liquid compared to gaseous water feedstock. When low current densities are required then the use of water vapour ma be preierable compared to liquid water as the feedstock * However, the relative I niidity ( M) of t e gas stream is esreeied to ha e a &xmg Im act on the operation of the sir-fed wate spfkt.bg system. M re ve , the delrydratton o the membrane should be avoided since this impacts the i tiic It has beeu s o n, for acidic electrolysis s s ems, that when low l values are at the cathode side, Che eleetrol ex performed somew a better, a r sul which as expected sfsce the dc ;ot¾posiiion of l¾0 Moleeules oceans at the istiode side in acidic eleetroiy¾is systems * The eto:, igh water concentration should be maintained in t he anode side< This Is only the case when the operatioos are done irsing acidic Ion exchange ma erial , We ocus kit not limit on alkaline m\< exchange ma e ials as solid electrolyte, as Barth-akradant catalysis generally a e less stable la acid enviroranent The influence of film thickness, relative humidity and temperature on Ionic and water transport and product gas permeability has iniportarit eonse nenees for the final device architecture. As is clear fr m Figure I and eqn, (1 } and (2), there is a net consumption of water a the cathode. t^r from, ambient ah at the anode can diffuse trough the IB to the cathode side, Keeping the 1E of the mr-fad F¥-E ceil hydrated may prove critical in its development Tlwefbre, a strategy con sts of incorporating water capturing materials in the IB or in the cathode eo ¾ia m t itself

Anode: _→ 2H ₂ 0 + (¾ - e~ 0)

Cathode; 4M ₂ 0 ¼~ -* 40H~ - 2H ₂

There are Ir leations, base m previous experimental results ami eiee roiyser models using Biitier - Volmer kinetics, that increased temperature leads to higher current densities for a given applied bias." ⁸ Additionally, greater water content is present in fully honiidified gas at higher teniperatnre, which may raise the Ihimmg current density of electrolysis S Stairted by water vaporm As discussed pevlo sly' , water management and hydration of the membrane ¼eame m mi y critical at higher operating temperatures with RH <l( Bi. , result;, tb& membran was dehydrated and consequently resnliiiig in a large decrease in the electrolysis current density. There oro, targeting a» operation with water vapour at higher te ei¾nn s requires either a scheme to keep the enihrane hyd ated o the use of an aherimiive lonorner that is les sensiti ve to its water content

Fo keeping the cathode sufticieutly hydrated and the operation of the device at sufficient temperatures _* a eiMes!g ed te mte and hydration management system stmtegy is provided: a) at the solar cell level, existing solar eel I technologies r ide the required potential to drive the water splitting reactions while allowing su eient light to pass, b) a radiation- absorbing «ta«f*t provides the requ r d fumper&ture m orde to feat u «} a femsaWe water sorption material which are used hi order to provide enough hydration to d) se ion exchange ma eral and e) at the IBM, a day/alght altering operation take pl¾c to dehydrnte/fehydrate the membrane by reversible water sorption mate ia whJks hydrogen is produced by solar water splitting during the cla ^f <

a)

For pnwidlng t e voltag which is required so as to drive the water splitting e cti n existing solar eel! technologies a * he us d. Apa t from the output voltage, allowing sufficient light to pass ia order to heat up the heat absorber/collector Is m additional prere u ite. This is done either at the solar eel! l vel or at the module level. At the eel! level, va i us sola eel technologies with the ri ibilities ranging front 209 ««t thick crystalline silicon (c~Si) water based solar cells with e$!cien«ks up to 1S~20% to te-film inorganic (anwphoo and mkiOc j^tallk silicon) or organic solar ^' cells with eil eneles between 6-1 % could h wed (M. A, Green et al, "S&tiir mil gffick y tehks (Verskm 45)™ _f l¾og, Phon o!t R s, AppL 23{i) _s 1-9 (2015 < ,

At the module level and for c-Si wafer based technologies, the sola cells are noroialiy connected in. series {Figure 2, displayed under number 3} and they are encapsulated in a configuration including glass (Figure 2» displayed under num er I) and EVA (ethyl vinyl m&M&y (Figure 2, displayed nnder somber 2), Instead of the tedlar (polyvinyl fluoride film) back sheet normally placed on the back side, we use a material that acts as the radiation- absorbing element a f nction w cfe is described in details hi the following seetioa With the operating temperaiine of a .module being the balanc between a) the beat roduc d by the module which depends on the operating point of the module, Its optical properties md the packing density of the cells, b) me heat los to the environment via conduction _* convection and radiation and c) the ambient operating temperature, we use a relaxed solar eel! packing densit ^ Le, the area of e m dule that m covered with solar cells com ared to that which is blank, for enaMing the highest rxxsslble besting of the heat collector. Therefo re, photons with wavelengths covering the full, solar speetru roay be sed to heat up the element radiation^absorblng element (Figure 2, ):

The purpose of the radiation-absorbing element is twofold, On one hand, it cools down the FY module and therefore improve its electrical ps ozm s®. On the other hand, i collects the thermal energy which is pttxi eed and which would have olherw.se been lost m heat to the environment. Instead of losing this energy, we use it to heal up a radiation-absorbing element

1? ((Fiiguuree 22,, 44)), _t aa m conmc&eptt wwiinncchh IIss ttaakkeenn aaddvvaannttaage ooff i inn tteecchhnnoollooggiieess m suechh m as tthhee W FY¾itihermmat hhyybbriridd s syysstteemmss.. l T¾hee n .ni^iliiattiOToiM-aiibmswfebinngg eelleemmeenntt peerfrfoorrmrsss t thhrreeee f Ikunsccttiioonnss:: ii)) aabbssoorrb tthhee iiii)) e coosndduuectt t tkhes aabbssoorrbbeedd hheeaatt iinntto tthhee rreevveerrssiibbllee wwaatteerr s soorrppttkiovnnft ms&atteedriaall ((FFiigguurree 2*» 5 S)) aannidl ffiilniaallllyy i illll)) lloossee aa mmiinniimmuum aammoouunntt ooff hheeaatt bbaacckk ttoo t thhee eennvviirroonnmmeenntt. MMaatteerriiaallss wwiitthh higgh m rad&i&atkiomn aahhssoorrppttaanneeee aamnd! h hiigghh t thheerrmmaall c coonndduuccttiivviittyy,, nnoorrmmaallllyy u usseedd mm tthhee FFVVfftt hhyybbrriidd ssoollaarr d deevviicceess,, ssucchh aass c coopppeerr,, aalluummiinniiuumm,, iirroonn,, ssttaaiinnlleessss s stteeeell eettcc,, aarree ccoonnssiiddeerreedd _*

The t vemfele water sorption mate h materials are n¾eso ^» or miem ^« rx>rous materials such m carbon, silica, m lecul r sieves, zeol tes o metal organic framewo ks (MOP) or a combination thereof

The materials are synthesized and tuned s such that they are able to adsorb and desorb water at the RH and T values of the specific geographic location (changes In climate). This can he achieved by eornb uatkM of difeoni materials or by suriaee modtliea&s or change m pore ske distributioa. An ideal nmterial can he described as follows (Figure 8). At l w EH values the material must adsorb water molecules MitldeniSy last to hecotne saturated wit water over the duration of one night ( 10 h}< For dc >t i u the material must b able to desorb Its water ca acity already at relatively high RH values, in order to keep RH in the reaction chambers high during the day, TemperamreKtriven hysteresis between adsorpiiou and desorptlos must be as Irn z as possi le to maintain a large water capacity _* That is, adsorption will omxt during gh at m er tti e below 20 *C wsd desorption will occurring dining the da noder imidiahon, at a temperature likely higher than 30 °€, The temperature increase shifts the water sot tka isotherm to lower water contents and e«haucestiesorptkm Mne los, ⁹ The kinetics of the ad- and desorption process must he sn eiently fast as to keep ihe eieelToiysls s stem saturated with vapour at ail times. In reality, no nmie as described In Figure B exists. In practice, auy material which adsorbs water at KB helow 8 % and desorhs water at RI$ above 7® % can be used.

Such reversible water sorption material cm also he used as a drying agent when teinperatees arc so low that host becomes an issue, 1¾ls can protect the device from damage due to expansion of water Into lee cry stals,

e) ¾n _[y e¾c¾a¾i^e ma^rials Figure 3 )

The Ion exchange ruatcrials can be alkaline membranes such as Fumasep FAB (Fu aiech), FAA-3-ΡΚ.-·.! 30 (Ftmtatech), A X { Astom), AHA (Astoni), l can be any materials based on a polymer backbone combined -with cation exchange groups such as ammonium, phosphoniuni or sulfonilim grd¾ps The ion exchange material can also be an aeidic membrane such as -Nafiom,. otlier peiiltiorinated polymers, suifonated h droeai-bons or yet other equivalents,

d) IEM day/ftight operation (fig.2):

The adsorption and dssorpiion is: regulated by a change in temperatiue aiid of the relative humidity i the cathode chamber. This can be achieved by the natural change in temperature and relative humidity of a day/night cycle (Figure 2, displayed under numbers 15-18):

1 ) Day: Operation

During the day, light not absorbed by the solar cell (Figure 2. displayed under number 20;) is absorbed by the thermal collector (Figure!, displayed under number 4) which directs its heat to the reversible water sorption material. The reversible water sorption material (Figure 2 ₅ displayed under number 5), situated in the closed reduction chamber (Figure 2, displayed under number 6), starts to heat u and releases its water to the reduction chamber due to a dro in RH and/or a shiit of its water sorption character stic^ tliereby increasing the local relative humidity, As water is; consumed at the cathode (Figure 2, displayed under number 7) in alkaline water splitting, the increase in RH ensures a constant suppiy of water , in acidic water splitting the same concept ca be used with. the reversible water so ption material connected to the anode chamber.

SirnultaneQUsly the water oxidation chamber (Figure 2, displayed under number 1Q) is closed to the ambient environment . Depending on the location^ the RFI of the ambient air is lower o equal to the RH of the cathode chamber. When. RH is low, water from there chamber is drawn to the water oxidation chamber by electro-osmosis through the membrane (Figure ¾ dispiayed under number 8¾ thereby wetting it and ensuring its ionic conductivity; In ad itiohj water is formed as the reaction product at the Water oxidation com locally wetting the membrane. The water is produced from hydroxide ions originating from the reduction of water molecules at the f eduction compartment

2) Night: Regeneration

During the night, RH increases and temperature drops. Additionally, no light is absorbed and thus the thermal collector (Figure 2, dispiayed under nuttibeir 4) is at ambient temperatuie. The K!YersiWft wafe sorption material · (Figure. 2, displayed under number 5) starts to cool down, RH starts to increase an when the oxidation chamber is open to the amMeiit eiivitOnmeat, the sorption material draws in water from the ambient air, by diffusive transport through the membiarte, ue to a difference in R& This way, the reversible water sorotios material s aoie to regenerate with water for operation during the day.

The produced hydrogen will likely be saturated with water (S0% RH at 50*0 , iram this will be lower when compared t conventional electr lysis (1 0% at %(Ψ€). For .farther use. of the produced hydrogen, it is prsierred for the hydrogen to be partially or completely dry, In g&o&er blem t of the invention,, the hydmgei* producing chamber be e uip ed with a pressure relieve val e, This valve cart open upon an increased pressure nside the hydrogen producing chamber due to nc ease in hydrogen partial pressure. This pressure relieve valve is a way of coll cti hydrogen from the eon^arirnen! and ifi another embodiment his valve can he opened and dosed man all with a regulator or actuator. I» another -embo^kaeB^ this pressure relieve valve is m its turn competed to ari intermediate ckunher with another re versible water sorption material mside. The purpose of this chamber ,1s to partially or com le el dry the produced hydrogen for farthe «se in e.g. a t¾el eeit in the description provided herein, numerous specific details are set forth. However, it is inulersto d that embodiments of tJhe Invention m e practiced without these specific details. In other ksianoes, welMmown methods, structures and te«hnioues have not been shown in detail its order not to obscure an raderstandiug of this description.

Other einbodiriients of the invent on will be apparent to those skilled in the art fro.ro consideration of the speelfieatioo and practice of the hwetiion disclose herein,

it is mteoded that the specification and examples he considered as exem la y only.

Each and every claim is incorporated into th specification as an embodiment of the present invention. Thus, the elairns are part of the description and are a farther description and are i addition to the preferred emb d ments of the present invention _*

Each of the claims set oat a particular embodiment of the in vention.

The following terras are provided solely to aid in the understanding of the h ention.

Particular and efk e aspects of the invention are set out in the aecompanyiag independent and dependent dakis _* Features from the depende t claims m y he combined th features of the independent claims and with features of other dependent claims as appropriate and not merely as explicitly set out i the claims. Thus, the claims following the detailed descr p i n are hereby ex ressly Ittcojrpotseed Into m$ detailed description, with each claim standing on its wn as a separate embo iment of tins hrvention.

2 _* 4 I&atnpies

Isaaapfc li Va on w» water electrolysis at high BM

A vapour $msc ater electrolysis experiment was performed -usin the possible ambodimerfis of the ¾av«atk«i. A Mc b ae electrode assem ly consisting of nickel (Ni) loam the anode material, fbsm as the cathode material and mk exchange Membrane (FAI PBT«I3% i¾nasen> were combined to form a m mbrane electrode assem ly (MBA). This EA was tested for water electrolysis a 00% I I ! fey c clic voltamtaetry, Figure 6 shows the resnlt of this experiment A current densit of 10 A C can be achieved at a applied potential of 2.09 V,

Example 2t Silica gel as reversible water orption material

Silica gel was tested as a reversible water sorpti n material (Figure 6). In a magnetic snspeps on b lance (MSB), silica gel _. powder (SO 239) was placed m dry conditions. An as made SO 239 as well a calcined SO 239 were tested Both mesopomus SO samples bad a pore s½c of 1.0.25 ftffi, The RH vahte as ehaaged over time and the change in weignt was mensnred, The calcined sample showed reduced water capacity which is likely dne to a decrease in surface silano groups.

m BRIEF BESCEiF lON OF THE BREWI GS

The present it eniiofi will become more fully nnderstood from the detailed description given herein below and the accompanying dra ua which are gi ven fey way of illostratinn only, aid thus arc sot limitative ofths present nvention, an wherein;

Fignre ! > demonstrates the chemical reactions m an alkaline anion exchange Materials,

Figure 1. Features of the app¾¾ratus 1 - l s 2 ^;« «ucaps latiori material, to instance light t¾¾ns 5arent itmikt t or matrix; 3~p otoYo!taie ^* 4™f leat absorber or heat sink; S ^s;; rever$ih!e

24 water sorption maerial b^dssetion gas t iti ?~rsducbou poto cathode; 8Non exe&ange material; oxkteiio ew anode; 10™ox<½tio as nnit; 11 -inlet atmospheri air; 12^ntiet for oxygen emiched atmospbedc air dwmg day; IS-eduetfen rodu t .H-mfeo on nro4«e collection otJiJei

13ay fet <^m mi of the mfofa 15 ^™ Air ciraa on during the oight at high ¾H and low T; 1 - mass trarispori at igh m to 6 daring night for adsorption oft*ater by S _: : alt cbsulatlon toiag day at lower Ι ί ami higher T >ntpared to IS; lHiigh Ml by wate desor tlon ¾* 5 at high T due to ontact wjrb 4 during day, W ^m light «&d ¼8 ab b¾i by the sok cells, 20 - Ight radiation for instance iufrsred absorbed by the beat absorber o beat sink (4).

Fi ure 3, Exampe of water adsA ikm e$i kJ8 Isotherm sillea gel R< $. Mikhail and F< A, ShehLJ Coi idMerfaceSci, 197 34 _» 65-75, ^je Figure 4. Ex m le of water isottem on 3 slica gels, X. LI, Z, U, Q, Xia and H. XL Ap≠ Therm, Eng„ 2007, 37, ¹¹

Figure 5. Example of water adso tjoa¾e.sirptio« Isotherm en silica get $L S. W, Skg and 1. B> Madeley, J, Chem, _t 19544, 365368. ef ences to tbe application

1) Ayers, &.< E<; Andeson E fL; Capaaao,€, ^' <; Ca er, B. D„; Ballon* L< T<; Harriots, G,;

Maaco, h; Mit^wieeki, M. Research Ad ancs owards Low Cost, High ES eney FEM Electrolysis, ECS Tram, 2§Ib, 33 (1% 3-15,

(2) ium&ri, S, White, R, Kumar, , Spvtrgeers, M. Solar Hydrogen Production from Seawater Yao? Electrolysis. E rg? Bmmm, &έ 2$½ % 1 25-1733,

(3) Sathre, R»j Scown, C, D. Moxr w, W. R,; Stevens, I, C; Sharp, L t)<; Agar, .; aleaak, , A.; Houie, . a, Gresaiatt, L . Llre-Cyeie Net Energy Assessment of Large-Scale Hydrogen Pr duction via Fhotoeleetr<K>hemlcai Water Splitting, Emrgy Emi Set 281 » 7 (10), 3264-3278,

(4) Naughton, M. S,; Bnsshett, F, R enis, P, J, A. Carbonate Resilience of lowin Biectrolyte» as«d Alkaliae Fnei Oils, J. P& r Smitcm 2 l _t 196 (4), V6 "d B,

(5) Lng, y.; CheB, O.j Memi , A. J>; Ti he, T. Hicfeer, , a,; ang, C< Y. Solid- S e Water Electrolysis wi th an Alkaline Memtmm, - Am€hem> 2912* 134 (22 (§) Sjsirgeoa _* J, M<; Lews, N. S. roon Exchange Monibraos Elec oysis Susained b Water Vapor. EmrgyEmwmt Set 2011 _» 4 ( 29* >

{?)· Gmmw? _* S< D Fox, E. B>; Ekwtoskw , A. A, Proton E&ohaage M«mbm»o (PEM) Electrolyser Operation under Anode Liqud and Cathode Vapor eed Conigi^tioas.

Mi ,1 Hynigmi Energy 34 (\6), 6D3 -660S>

(8) S&wada> S..; Yamsk T,; Mae«o< T.; A$am M : Suzuki, A>; Tern** T &ekawa _* Y _* Solid Polymer Electrol vte Water Mee&olysis S stem t¾r Hydwg-a* Prodi*etio» ased o» Our Newly Developed M m rnes, Part Ϊ: Analysts of Voltage-Currant Characteistics. P g. Nml Emr$y im SQ (2-

(9) Kis», ¾4 Yan , S Rao, S. R.; ^' Nmty m^ S.; ap stlft, B. A4 Futtska a, H. Ornate, A, S<; Yagh!, 0. .; Wang, E. N. Water Harvestin orn hit w i Metal-Orgnk Fi»©woik§ Powsssd b Natural SsHiligbk Sckme 2017, (April)* 1-10.

(III) Mlklmll, E. S<; SheM, F. A< Adsorpiios m Relation to Pore Structures of Silicas II. Water Vapor Adsorption Wide-Pore and Mi tp ms Silica, des, J. hkifmeri e Sl i ,34(i% 65-75.

(I I) Li, X Li, Z>; Xia, Q4 Xt _> H. Effects of Pore Sizes of Porous Silica Gets on f^sopiion AeU atkm gf of Water V¾so« f¾»£ Therm. Eng.207, 27 (5~<¾ 86$~8 &

(1.2) Sisg, _* S. W ^' Madeley, IX The Swfk« Properties of Silica (Ms- X A$ tptkm of Water Vapour, ?Ι. Otat 1954, (7%