Superhydrophilic CoFe Dispersion of Hydrogel Electrocatalysts for Quasi-Solid-State Photoelectrochemical Water Splitting

Photoelectrochemical (PEC) water splitting is an attractive strategy to convert solar energy to hydrogen. However, the lifetime of PEC devices is restricted by the photocorrosion of semiconductors and the instability of co-catalysts. Herein, we report a feasible in situ inherent cross-linking method for stabilizing semiconductors that uses a CoFe-dispersed polyacrylamide (PAM) hydrogel as a transparent protector. The CoFe-PAM hydrogel protected BiVO₄ (BVO) photoanode reached a photocurrent density of 5.7 mA cm^–2 at 1.23 V_RHE under AM 1.5G illumination with good stability. The PAM hydrogel network improved the loading of Fe sites while enabling the retention of more CoFe co-catalysts and increasing the electron density of the reaction active sites, further improving the PEC performance and stability. More importantly, by tuning the polymerization network, we pioneer the use of quasi-solid-state electrolytes in photoelectrochemistry, where the high concentration of ionic solvent in the PAM hydrogel ensures effective charge transport and good water storage owing to the hydrophilic and porous structure of the hydrogel. This work expands the scope of PEC research by providing a class of three-dimensional hydrogel electrocatalysts and quasi-solid-state electrolytes with huge extension potential, and the versatility of these quasi-solid-state electrolytes can be employed for other semiconductors.