A NiCoP–graphene hybrid electrode supported on three-dimensional nickel foam (NiCoP–Gr/NF) was successfully fabricated and evaluated for the hydrogen evolution reaction (HER) in alkaline media. The electrode was prepared via a two-step process involving electrophoretic deposition of graphene onto nickel foam followed by phosphidation, enabling uniform incorporation of graphene within the bimetallic NiCoP matrix. Structural and surface characterizations (SEM, EDX, XRD, Raman spectroscopy, and XPS) revealed a homogeneous and porous coating composed of ultrafine NiCoP nanoparticles tightly anchored on wrinkled graphene sheets across the nickel foam framework. Electrochemical testing in 1 M KOH demonstrated an overpotential of 168 mV at a current density of 10 mA cm⁻2 and a Tafel slope of 48.9 mV dec⁻1, indicating fast HER kinetics. The improved catalytic performance is attributed to the synergistic interaction between NiCoP and graphene, which enhances charge-transfer efficiency, increases electrochemically active surface area, and promotes efficient electrolyte diffusion within the three-dimensional porous structure. These results demonstrate the effectiveness of the NiCoP–graphene hybrid architecture as a robust and efficient electrode for alkaline hydrogen evolution.
NiAl₂O₄ spinel was synthesized by a co-precipitation method and evaluated as an electrocatalyst for the hydrogen evolution reaction (HER) in alkaline media. Structural and surface analyses confirmed the formation of a phase-pure, well-crystallized spinel with defect-rich surface oxygen species. Electrochemical measurements in 1.0 M KOH revealed clear Ni2⁺/Ni3⁺ redox activity, low charge-transfer resistance, and favorable reaction kinetics. The NiAl₂O₄ electrode exhibits an onset potential of about 0.207 V vs. RHE and a Tafel slope of approximately 204 mV dec⁻1, indicating a Volmer-dominated HER mechanism. Stable hydrogen evolution was achieved with a production rate reaching 814.32 µmol·h⁻1. These results demonstrate that NiAl₂O₄ is an effective noble-metal-free electrocatalyst for alkaline hydrogen evolution.
High-entropy oxides (HEOs) offer a versatile platform for photocatalytic applications due to their compositional flexibility and structural stability. In this work, a series of A-site high-entropy spinel oxides with the formula (Mg0.2Co0.2Ni0.2Cu0.2Zn0.2)B2O4, (BAl, Cr, Fe, Mn) was synthesized via a modified co-reduction and oxidation route. The role of B-site cations in modulating structural, optical, and photocatalytic properties was systematically investigated. All compositions exhibited single-phase cubic spinel structures with increasing lattice parameter, microstrain, and cation inversion from Al to Mn. Optical characterization revealed progressive band gap narrowing from 2.66 eV (HEO-Al) to 1.94 eV (HEO-Mn), consistent with enhanced p-d hybridization and lattice distortion. Mott-Schottky analysis confirmed n-type conductivity and a cathodic shift in flat-band potentials, indicating improved electron transfer capacity. Under visible-light irradiation, the photocatalytic degradation of Rhodamine B followed the trend: HEO-Mn > HEO-Fe > HEO-Cr > HEO-Al. HEO-Mn achieved 85.20% degradation efficiency and the highest apparent rate constant (0.075 min(-1)), attributed to its narrow band gap, high donor density, and favorable redox properties. Scavenger experiments identified superoxide radicals (center dot O-2(-)) as the dominant reactive species. These results highlight B-site engineering as an effective strategy for optimizing the photocatalytic performance of spinel HEOs and offer new insights for the design of visible-light-responsive materials for environmental remediation.
Stainless-steel coatings were fabricated using the arc-wire spraying technique and assessed for the first time as electrocatalysts for the hydrogen evolution reaction (HER) in alkaline media. Coatings were deposited on sandblasted mild-steel substrates using optimized parameters (30.9 V, 135.9 A, 3.1 m min⁻1 wire feed, 4.8 bar air pressure, 140 mm spray distance). EPMA–WDS and XRD analyses revealed a dense lamellar structure composed of Fe–Cr–Ni metallic phases with minor Fe2O3 and Cr2O3 inclusions. Nanoindentation showed high mechanical performance (H ≈ 3.76 GPa; E ≈ 100 GPa) and strong interfacial adhesion. Electrochemical testing in 1.0 M KOH demonstrated a low η₁₀₀ potential of 0.19 V vs. RHE, a Tafel slope of 0.76 V dec⁻1, and a hydrogen evolution rate of 1181 µmol h⁻1, confirming efficient catalytic activity and stability. These findings establish arc-wire–sprayed stainless-steel coatings as robust, scalable, and cost-effective electrodes for HER.
The development of efficient and sustainable photocatalysts for hydrogen generation is a key step in addressing the global energy and environmental crises. In this study, spinel ferrite nanoparticles with the general formula MFe2O4 (M = Mn, Ni, Cu) were synthesized via a facile co-precipitation route followed by thermal treatment, and their physicochemical and photocatalytic properties were systematically investigated. Structural analysis by X-ray diffraction confirmed the successful formation of phase-pure spinel ferrites, whereas SEM and EDX revealed distinct morphological features and uniform elemental distributions in the manufactured samples. Raman spectroscopy provided evidence of cation-dependent lattice ordering, and UV–Vis diffuse reflectance measurements showed band gap values of 1.32 eV (MnFe2O4), 1.43 eV (CuFe2O4), and 1.78 eV (NiFe2O4). Photocatalytic H2 evolution experiments under visible-light irradiation demonstrated that MnFe2O4 exhibited a superior capability, reaching nearly 150 μmol of H2 within 25 min, outperforming NiFe2O4 by 1.36 times and CuFe2O4 by 2.14 times. The superior photocatalytic ability of MnFe2O4 can be attributed to its narrower band gap, porous morphology, and enhanced structural order, which synergistically promote visible light absorption, charge segregation, and surface redox reactions. This comparative study highlights the pivotal role of cation substitution in tailoring the electronic and structural properties of spinel ferrites and establishes MnFe2O4 as a highly promising photocatalyst for cost-effective and environmentally friendly hydrogen production.
