NiCo2S4 cocatalyst supported Si nanowire heterostructure for improved solar-driven water reduction: experimental and theoretical insights

We report a heterostructure photocathode composed of the optimal gradient of nickel cobalt disulphide layers (NiCo2S4 NS) over a p-Si nanowire (Si NW) surface designed for the solar-assisted water reduction process. The optimal Si NW/NiCo2S4 NS heterostructure exhibits enriched solar water reduction activity with a photocurrent density of 15 mA cm(-2) at -0.8 V vs. RHE applied bias and an onset potential of 301 mV vs. RHE under simulated solar irradiation. Moreover, the fabricated heterostructure photocathode (Si NW/NiCo2S4 NS) at the applied bias of -0.3 V vs. RHE produces a hydrogen gas evolution rate of around 53.75 mu mol cm(-2) h(-1). The accomplished catalytic activity of the heterostructure can be attributed to the HER electrocatalyst properties of NiCo2S4 as an interfacial layer, such as interfacial energies, charge transfer kinetics, and solar-driven water reduction activity at the photocathode/electrolyte interface. An electrochemical impedance spectroscopy study demonstrates a significant reduction in charge transfer resistance that results in rapid electron transfer at the interface for efficient charge separation and migration processes. The density functional theory calculations reveal that NiCo2S4 NS has a suitable electronic band alignment with a water redox potential advancing the catalytic efficiency owing to barrier-free electron transport with near-zero Gibbs free energy of hydrogen adsorption on hetero-interface sites (Delta G(H*) = 0.02 eV at Co1 site). Consequently, the proposed heterostructure scheme is a promising strategy for designing a high-performance Si photocathode for solar water reduction.

Automated summary

We have developed a heterostructure photocathode consisting of nickel cobalt disulphide layers (NiCo2S4 NS) over a p-Si nanowire (Si NW) surface for solar-assisted water reduction. The optimized Si NW/NiCo2S4 NS heterostructure exhibits enhanced water reduction activity under simulated solar irradiation. The catalytic performance of the heterostructure is attributed to the electrocatalyst properties of NiCo2S4 and efficient charge separation and migration processes at the photocathode/electrolyte interface. Our findings demonstrate the potential of this heterostructure scheme for designing high-performance Si photocathodes for solar water reduction.