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

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