Efficient Photoelectrochemical O₂ and CO Production Using BiVO₄ Water Oxidation Photoanode and CO₂ Reduction Au Nanoparticle Cathode Prepared by In Situ Deposition from Au³⁺ Containing Solution

Abstract The cathodic polarization of various conducting electrodes in a CO₂‐saturated DMF/5% H₂O solution containing AuCl₃ (DMF = N,N‐dimethylformamide) results in in situ deposition of a highly selective and efficient CO₂ to CO conversion Au nanoparticle electrocatalyst. These electrodes include glassy carbon, fluorine doped tin oxide (FTO), and Au plate. The efficiency of the Au nanoparticles is enhanced by introducing 1‐ethyl‐3‐methylimidazolium trifluoromethanesulfonate ionic liquid (EMI OTf IL, 10%) to the AuCl₃‐containing DMF/5% H₂O deposition solution. In addition to the simplicity and novelty of the preparation method, the resultant in situ deposited Au nanoparticle cathode shows superior activity and selectivity for CO₂ to CO conversion compared to Au nanoparticles prepared by other techniques. Moreover, the in situ deposited Au nanoparticle electrode is used as a cathode in an n‐type photoelectrochemical cell with a water oxidation BiVO₄ photoanode modified with three‐layer water oxidation catalysts [FTO/EMI BiVO₄/FeOOH/NiOOH/Co(bpy‐P)₂, bpy‐P = 2,2′‐bipyridine‐4,4′‐diphosphonic acid] to achieve efficient solar‐assisted CO and O₂ production with 0.78% solar to CO conversion efficiency. The resultant 0.78% efficiency is the highest efficiency obtained toward CO₂ to CO conversion in PEC devices without any use of photovoltaic cell as a tandem.