A water photoelectrolysis cell with a liquid-liquid phase boundary

Oxygen was generated at 0.4 volt below the equilibrium potential of the electrode reaction,(UNFORMATTED TABLE OR EQUATION FOLLOWS){dollar}{dollar}rm 2Hsb2O = Osb2 + 4Hsp+ + 4esp-eqno(1){dollar}{dollar}(TABLE/EQUATION ENDS)which is the largest undervoltage ever reported. This was achieved by mediating the photoelectrooxidation of water via the sequence:(UNFORMATTED TABLE OR EQUATION FOLLOWS){dollar}{dollar}eqalignno{lcub}rm 4Clsp-&+rm hnu = 2Clsb2 + 4esp-&rm(1a)crrm 2Hsb2O&+rm 2Clsb2 = 4Clsp- + 4Hsp+ + Osb2&rm(1b)cr{rcub}{dollar}{dollar}(TABLE/EQUATION ENDS)Reaction 1a occurred at layered semiconductor photoanodes immersed in judiciously selected organic solvents (such as nitromethane) which were in contact with an immiscible aqueous phase where Reaction 1b took place in the presence of a heterogeneous catalyst. Concentrated tetrabutylammonium chloride was dissolved in both liquids and served as the source of the Cl{dollar}sb2{dollar}/Cl{dollar}sp-{dollar} mediator redox couple. Molybdenum disulfide photoanodes yielded solar energy conversion efficiencies of three percent, using the terrestrial spectrum consisting predominantly of visible and infrared radiation. The photocorrosion resistance and durability of molybdenum disulfide anodes were remarkably enhanced by the adsorption of chloride ions at the electrode surface. The reaction(UNFORMATTED TABLE OR EQUATION FOLLOWS){dollar}{dollar}rm 2Hsp+ + 2esp- + hnu = Hsb2eqno(2){dollar}{dollar}(TABLE/EQUATION ENDS)has been documented in the literature at efficient indium phosphide photocathodes. Thus the cell(UNFORMATTED TABLE OR EQUATION FOLLOWS){dollar}{dollar}eqalign{lcub}rm n{lcub}-{rcub}MoSsb2(s)vert 1M(Csb4Hsb9)sb4NCllbrack CHsb3NOsb2rbrackVert 1Mcrrm(Csb4Hsb9)sb4NCllbrack aq,pH4rbrack vert p{lcub}-{rcub}InP(s)cr{rcub}{dollar}{dollar}(TABLE/EQUATION ENDS)will provide prospective means for the future production of hydrogen fuel by the photoelectrolysis of water.