Enhancing Photoelectrochemical Seawater Splitting Efficiency by a Dual-Strategy Approach of W Doping and CoOOH Layer Deposition on BiVO₄ Photoanodes

Photoelectrochemical (PEC) seawater splitting offers a sustainable pathway for hydrogen production, yet its practical application is hindered by sluggish reaction kinetics and severe photocorrosion in chloride-rich environments. This study presents a dual-strategy modification of BiVO₄ photoanodes through tungsten (W) doping and cobalt oxyhydroxide (CoOOH) nanolayer deposition to synergistically enhance the PEC performance and stability in natural seawater. W doping optimizes the electronic structure of BiVO₄ by reducing the bandgap from 2.4 to 2.35 eV and increasing carrier concentration from 1.41 × 10²¹ to 3.31 × 10²¹ cm^-3, while CoOOH acts as a dual-functional layer that suppresses surface recombination via oxygen vacancy formation and protects against chloride-induced corrosion. The optimized CoOOH/W-BVO photoanode achieves a photocurrent density of 3.77 mA cm^-2 at 1.23 V vs reversible hydrogen electrode (RHE) with 96 h stability in natural seawater, outperforming pristine BiVO₄ by 150% and single-modified counterparts by 40-60%. Mechanistic analyses reveal that W⁶⁺ substitution elongates V-O bonds, thereby enhancing the bulk charge separation. Concurrently, CoOOH facilitates hole extraction through oxygen vacancies, with oxygen vacancy content increasing from 3.9% to 24.3%. The dual modification also reduces interfacial charge-transfer resistance to 94.44 Ω and shifts the flat-band potential negatively to 0.15 V vs RHE, improving light absorption and charge utilization efficiency (applied bias photocurrent efficiency (ABPE) of 0.95% at 0.77 V). This work provides a robust strategy for designing efficient and durable photoanodes, advancing marine-resource-utilized renewable energy technologies.