Aging Ni(OH)₂ on 3C-SiC Photoanodes to Achieve a High Photovoltage of 1.1 V and Enhanced Stability for Solar Water Splitting in Strongly Alkaline Solutions

Photoelectrochemical (PEC) water splitting is a promising approach to directly convert solar energy to renewable and storable hydrogen. However, the very low photovoltage and serious corrosion of semiconductor photoelectrodes in strongly acidic or alkaline electrolytes needed for water splitting severely impede the practical application of this technology. In this work, we demonstrate a facile approach to fabricate a high-photovoltage, stable photoanode by depositing Ni(OH)₂ cocatalyst on cubic silicon carbide (3C-SiC), followed by aging in 1.0 M NaOH at room temperature for 40 h without applying electrochemical bias. The aged 3C-SiC/Ni(OH)₂ photoanode achieves a record-high photovoltage of 1.10 V, an ultralow onset potential of 0.10 V vs the reversible hydrogen electrode, and enhanced stability for PEC water splitting in the strongly alkaline solution (pH = 13.6). This aged photoanode also exhibits excellent in-air stability, demonstrating identical PEC water-splitting performance for more than 400 days. We find that the aged Ni(OH)₂ dramatically promotes the hole transport at the photoanode/electrolyte interface, thus significantly enhancing the photovoltage and overall PEC performance. Furthermore, the oxygen evolution reaction (OER) activity and the phase transitions of the Ni(OH)₂ electrocatalyst before and after aging are systematically investigated. We find that the aging process is critical for the formation of the relatively stable and highly active Fe-doped β-NiOOH, which accounts for the enhanced OER activity and stability of the PEC water splitting. This work provides a simple and effective approach to fabricate high-photovoltage and stable photoanodes, bringing new premise toward solar fuel development.