Ammonium thiomolybdate ((NH₄)₂Mo₃S₁₃) coatings on N-doped carbon nanowalls as optimal and durable electrocatalysts for hydrogen evolution

Ammonium thiomolybdate (ATM - (NH₄)₂Mo₃S₁₃) represents a highly promising molecular precursor for hydrogen evolution reaction (HER) due to its high density of accessible sulfur edge sites. However, its practical implementation is limited by the poor adhesion, low conductivity, and structural instability of pure ATM films. In this work, an ATM layer was fabricated via a scalable spray-coating approach followed by low-temperature annealing (100 °C) on N-doped carbon nanowalls (N-CNWs) grown on a Ti substrate. The N-CNWs scaffold provides a vertically oriented, conductive, and porous framework that enables homogeneous anchoring of amorphous ATM clusters and enhances electron transport across the electrode–electrolyte interface. Structural and spectroscopic analyses confirm the amorphous phase of ATM as well as the intimate interaction between Mo–S clusters and the N-CNW network. The optimized electrode delivers an overpotential of ∼45 mV at 10 mA cm^-2, a Tafel slope of 82 mV dec^-1, and a turnover frequency of 1.28 s⁻¹ at −0.05 V vs. RHE, outperforming both bare Ti and Ti/N-CNW. The electrode demonstrates excellent durability, maintaining stable operation for 100 h at 10 mA cm⁻² and retaining 98% of its activity over 20 h at −55 mV. These results demonstrate that integrating of highly conductive N-CNWs with edge-rich [Mo₃S₁₃]^2--based ATM clusters offers an optimal strategy to enhance active-site accessibility, charge transfer, and long-term durability. This work presents a cost-effective and scalable approach to next-generation sulfur-based HER electrocatalysts.