d-Band Center Engineering of Nickel Nanoparticles Accelerates Water Dissociation for Hydrogen Evolution in Neutral...

While Pt is highly efficient for hydrogen evolution reaction (HER), its widespread use is limited by scarcity and high cost. Herein, a vertically aligned electrocatalyst is present comprising Ni₃S₂ nanotube arrays (NTAs) and Ni nanoparticles (NPs) (Ni₃S₂/Ni NTAs) for neutral HER. In a neutral 4 wt.% NaCl solution (pH = 7), the Ni₃S₂/Ni NTAs achieves a current density of 100 mA cm^-2 at a low overpotential of 540 mV, outperforming both Ni₃S₂ NTAs and Ni NTAs and even the commercial Pt plate. The hollow tubular structure offers ample mass transfer channels, and strong electronic interaction between Ni₃S₂ and Ni is observed. Theoretical studies reveal that the lowered d-band center (ɛ_d) of Ni 3d orbital significantly reduces the activation energy for H₂O dissociation and facilitates the movement of an H atom in H₂O away from OH to form a transition state, consequently promoting H₂ evolution. When Ni₃S₂/Ni NTAs is used as the cathode in a two-electrode diaphragm-free electrolyzer with a RuSnTi anode, efficient H₂ production and energy-saving Cl₂ evolution are achieved. This work highlights the potential of uniquely structured electrocatalysts for HER in neutral NaCl solutions.