A multifunctional vanadium-doped cobalt oxide layer on silicon photoanodes for efficient and stable photoelectrochemical water oxidation

Photoelectrochemical (PEC) water splitting is an attractive method to convert solar energy into chemical fuel. However, developing highly efficient photoanodes for PEC cells to meet industrial requirements remains a challenge. Herein, we effectively alter the onset potential of a photoanode though the doping of V into Co oxide film via the low-cost method of magnetron co-sputtering deposition on a p(+)n junction Si cell (p(+)nSi/CoVO). The highest photocurrent density of p+nSi/CoVO is 29.15 mA cm(-2) (at 1.23 V vs. a reversible hydrogen electrode (RHE)). Moreover, a successful decrease in the onset potential by 40 mV to 1.00 V (at 1 mA cm(-2)) and a 3.6-fold increase in the incident photon to current conversion efficiency (IPCE) are achieved compared to p(+)nSi/CoO. The p(+)n junction Si cell provides not only photoexcited vacancies but also a photoproduced voltage of 608 mV. We find that the doped V atoms are multifunctional: they can decrease the charge transfer resistance of the Co3O4 film, serve as a Lewis acid to increase the local pH value, and facilitate the generation of oxo-bridged Co-IV=O species to accelerate the kinetics of the oxygen evolution reaction (OER); therefore, they can obviously decrease the onset potential of p(+)nSi/CoVO in the OER. This work highlights a general approach to further improve the performance of OER catalysts via engineering active sites and the local chemical environment through element doping.