Synergistic Effect of MoO₂-Ni₃(PO₄)₂ Heterostructures In Situ Grown on Nickel Foam Enhances the Efficiency of Hydrogen Evolution Reaction in Simulated Seawater

Hydrogen (H₂) with a high gravimetric energy density (142 MJ/kg) and zero carbon emissions is a green energy source. The electrocatalytic hydrogen evolution reaction (HER) is a prominent strategy for hydrogen production, and the essential technology of electrocatalysts focuses on creating catalysts that are highly efficient, cost-effective, and excellently stable. Herein, a heterostructure electrode/catalyst consisting of MoO₂-Ni₃(PO₄)₂/NF (where NF = nickel foam) was fabricated using (NH₄)₆[NiMo₉O₃₂]·6H₂O as precursor via a two-step method utilizing hydrothermal synthesis and chemical vapor deposition (CVD). Thanks to the remarkable synergistic effect occurring at the interfaces of the heterostructure, the catalytic efficiency of MoO₂-Ni₃(PO₄)₂/NF can outperform that of other catalyst materials. In particular, the MoO₂-Ni₃(PO₄)₂/NF electrode exhibits overpotentials of 66 and 258 mV at 10 mA cm^-2, along with low Tafel slopes of 56.03 and 85.32 mV/dec in 1 mol/L KOH and simulated seawater electrolyte, respectively. Density functional theory calculations (DFT) validate that the Gibbs free energy (ΔG_H*) values for hydrogen adsorption of MoO₂ (110)/Ni₃(PO₄)₂ (−222) with 0.033 eV are much closer to zero, similar to Pt/C. In situ FTIR spectra indicate that the synergistic effect of MoO₂ (110)/Ni₃(PO₄)₂ (−222) can further create more catalytic active sites and modulate intermediate H* adsorption to promote the HER process. Overall, this study highlights the potential of nanostructured MoO₂-Ni₃(PO₄)₂ heterostructures for application in efficient hydrogen production under seawater conditions.