Exploring the Catalytic Efficiency of Atmospheric Plasma-Sprayed NiAlMo Coating across Varied KOH Electrolyte Concentrations

This study investigates an efficient Ni–Al–Mo ternary alloy electrocatalyst, fabricated via an atmospheric plasma spray, as a cost-effective solution for hydrogen production in alkaline media. The coating strategy combines the porosity-inducing properties of aluminum with the catalytic enhancement offered by molybdenum, aiming to improve both the hydrogen evolution reaction performance and long-term stability. To activate the catalyst, the electrode coatings were selectively leached to remove Al-rich phases, forming a porous structure with a high electroactive surface area. The impact of KOH electrolyte concentration (5.6–30 wt %) on the morphology, microstructure, and electrochemical behavior of the electrodes was systematically evaluated. Structural characterization revealed that increasing KOH concentration alters the distribution of intersplat pores, microdefects, and internal cracks, while intensifying Mo depletion and modifying the overall composition. These changes significantly influence the hydrogen evolution reaction performance and the degradation rate of the coating. The electrochemical tests at 60 °C showed that in 30 wt % KOH, the electrode achieved an overpotential of 39 mV at 200 mA cm–2 and a Tafel slope of 29.1 mV dec–1, reflecting high catalytic activity. However, this condition also induced rapid degradation due to corrosive dissolution. In contrast, operation in 20 wt % KOH resulted in superior durability, maintaining a stable voltage of −1.018 V over 500 h at 400 mA cm–2 without significant structural deterioration.