Nanowire/nanotube array tandem cells for overall solar neutral water splitting

• PEC tandem cell consisting of p-Si/TiO2/Fe2O3 csh-NW photocathode and TiO2/TiO2 cs-NT photoanode.
• p-Si/TiO2/Fe2O3 csh-NWs with significantly improved photocathodic performance.
• Annealing under nitrogen to further enhance the csh-NWs performance.
• Overall solar water splitting in a neutral pH water with a STH efficiency of ~0.18%.

In this study, we report the fabrication and characterization of a novel PEC tandem cell, consisting of p-Si/TiO2/Fe2O3 core/shell/hierarchical nanowire (csh-NW) array photocathode and TiO2/TiO2 core/shell nanotube (cs-NT) array photoanode, for overall solar water splitting in a neutral pH water. The p-Si/n-TiO2/n-Fe2O3 csh-NWs, made mainly by solution-processed methods, offer significantly improved performance in the neutral pH water with a low (positive) onset potential and photoactivity at zero bias, due to the increased reaction surface area, effective energy band alignment among p-Si, n-TiO2 and n-Fe2O3 enhancing the charge separation, improved optical absorption, and enhanced gas evolution. Nitrogen modification (annealing under N2) is used to further enhance the csh-NWs photocathodic performance. The PEC tandem cell is then able to handle overall solar water splitting in the neutral pH water with a solar-to-hydrogen (STH) efficiency of ~0.18%. The achieved results demonstrate initial steps toward the realization of full PEC devices using earth-abundant materials for solar hydrogen generation suggesting competitive performance when solar matched photoanode core material and co-catalysts are used.

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