Charge allocation and mass transfer efficiency during hydrogen evolution reaction in high salinity neutral...

Hydrogen production from high-salinity wastewater offers a pivotal strategy for carbon neutrality but is hindered by complex matrix effects in neutral media that create unfavorable interfacial microenvironments. This study systematically investigates hydrogen evolution reaction (HER) charge allocation and mass transfer mechanisms in distinct electrolyte matrices (SO₄^2-, NO₃^-, and Cl^-) using nickel foam (NF) electrodes. The results revealed a distinct electrode porosity dependence, wherein 80 PPI NF demonstrated superior activity, attributed to abundant active sites and active species formed in situ on the electrode surface that promote water dissociation. Critically, the Na₂SO₄ system yielded optimal catalytic performance with a Faradaic efficiency (FE) of 93.8% and exceptional durability (retaining 96.8% yield). This performance was driven by negligible kinetic competition, unlike other matrices in which cathodic charge utilization was compromised by competitive parasitic pathways and steric hindrance. In contrast, the NaNO₃ system performance was compromised by thermodynamic nitrate electro-reduction, while NaCl system suffered drastic degradation (FE dropped to 66.7%) due to parasitic electron scavenging via active chlorine redox shuttling and oxidative electrode etching. Density functional theory (DFT) calculations further corroborate that SO₄^2- imposed minimal electronic perturbation on Ni (111), whereas Cl^- induced an upward D-band center shift, leading to excessive hydrogen adsorption and kinetic suppression. Collectively, these findings elucidate matrix-dependent regulatory mechanisms, providing a mechanistic basis for optimizing charge allocation in the efficient conversion of high-salinity wastewater into hydrogen.