Nickel-doped graphene films on stainless steel as efficient hydrogen recombination catalysts

Abstract

Nickel-doped catalysts supported on graphene-coated porous 304L stainless steel substrates were synthesized and evaluated for hydrogen recombination applications. The substrates, with a pore size of 50 μm, were doped with nickel loadings of 0.25, 0.50, 1.0, and 2.0 wt%. SEM analysis revealed that low nickel contents (0.25–0.50 wt%) resulted in a cracked, graphene-dominated surface and high BET surface area (up to 5.28 m2/g for 0.5 wt% Ni), whereas higher loadings (1.0–2.0 wt%) promoted the formation of dispersed metallic and nickel particles, reducing the measured surface area. XRD patterns confirmed the coexistence of austenitic and martensitic phases, spinel-type oxides, graphene-related carbon phases, and nickel-containing phases (metallic Ni, NiO, Ni (OH) 2). Raman spectroscopy revealed a five-band model (D, G, D2, D3, D4), with characteristic modifications in defect density (decreasing ID/IG ratio) and distinct features near 500 cm􀀀 1 assigned to NiO, confirming the presence of metallic and oxidized nickel phases. No signals related to iron oxides or spurious nickel oxide were observed beyond these assignments. Water contact angle measurements demonstrated strong hydrophobicity (above 120◦) for all samples, with a slight decrease at higher nickel loadings due to partial masking of graphene surfaces. Hydrogen recombination tests showed that catalytic performance improved with increasing nickel content, achieving approximately 63 % hydrogen removal with only 1.0 wt% Ni. The combined effects of high surface area (BET), well-dispersed nickel nanoparticles, and the graphene coating contributed to enhanced catalytic activity, efficient gas diffusion, and high surface hydrophobicity. These findings highlight nickel-based graphene-supported catalysts as an effective and economically viable alternative to platinum or palladium for hydrogen recombination in gas-phase applications.