Ni2P nanocrystals modification on Ta:α-Fe2O3 photoanode for efficient photoelectrochemical water splitting: In situ formation and synergistic catalysis of Ni2P@NiOOH cocatalyst

The application potential of hematite (alpha-Fe2O3) photoanode for photoelectrochemical (PEC) water splitting is restricted by its poor conductivity and severe carrier recombination. Herein, a coupling modification strategy of tantalum (Ta) doping and Ni2P nanocrystals modification is developed to realize the simultaneous optimization of photocurrent density and onset potential of alpha-Fe2O3 photoanode. The resulting Ni2P/Ta:alpha-Fe2O3 photoanode exhibits a photocurrent density of 2.98 mA/cm(2) at 1.23 V vs. RHE, which is 2.76-fold higher than that of pristine alpha-Fe2O3. Characterization results show that Ta-doping improves the conductivity and carrier density, while Ni2P nanocrystals optimizes the hole injection efficiency and water oxidation kinetics of photoanode. Notably, Ni2P nanocrystals form a core-shell structure (Ni2P@NiOOH) in situ during the PEC reaction. Density functional theory calculations indicate that the adsorption sites for Ni2P@NiOOH cocatalyst are mainly Ni atoms at the interface between NiOOH and Ni2P, with adjacent Ni or P atoms from Ni2P core also participating in the reaction, and that the synergistic catalysis of Ni2P and NiOOH lowers the energy barrier for the key *OOH intermediates formation. Finite element simulations of the current density distribution show that Ni2P core with high conductivity exhibit a significant current-collector effect, accelerating carrier migration in Ni2P@NiOOH. This work contributes to the understanding of the catalysis of Ni2P-derived composite oxygen evolution reaction catalysts and provides a reference for the rational design of photoanode for efficient PEC water splitting.

Automated summary

A coupling modification strategy of tantalum doping and Ni2P nanocrystals modification is developed to optimize the photocurrent density and onset potential of hematite photoanode. The modified photoanode exhibits higher photocurrent density and lower onset potential, showing great potential for photoelectrochemical water splitting.