Graphene layers steer nickel foam toward more active oxygen evolution catalyst phase

Apr 25, 2026

Electrochemically exfoliated graphene directs nickel foam surfaces toward gamma-NiOOH during oxygen evolution, improving electrocatalytic efficiency and durability for hydrogen production.

(Nanowerk News) Researchers have developed a method to control how nickel-based electrodes reconstruct during the oxygen evolution reaction (OER), a key half-reaction in producing hydrogen from water. By coating nickel foam with electrochemically exfoliated graphene (EG), the team directed the surface chemistry toward a more catalytically active phase, improving both efficiency and durability for alkaline water electrolysis (Engineering, “Superior Electrocatalytic Oxygen Evolution of Nickel-Based Metals Modulated by Controllable Graphene Layers via Interfacial Redox Process”).

Key Findings

Nickel is widely used as a precatalyst for OER because it transforms under operating conditions into nickel oxyhydroxide (NiOOH), the species that actually drives the reaction. However, NiOOH exists in two main forms: beta-NiOOH and gamma-NiOOH. The gamma phase contains nickel in a higher oxidation state (Ni4+) and delivers better catalytic performance, but conventional electrode preparation methods offer limited control over which phase forms during operation. The research team, based at Zhejiang University and Dalian University of Technology, addressed this problem by using EG as a redox mediator. The graphene layers selectively oxidize the nickel foam surface to produce Ni2+ species that preferentially convert into gamma-NiOOH rather than beta-NiOOH during anodic polarization. (a) Schematic of the synthesis of the exfoliated graphene nickel foam (EG–NF). GF: graphite foil. (b–d) Scanning electron microscopy (SEM) images of (b) NF and (c, d) EG–NF. (e) X-ray diffraction (XRD) patterns, (f) Raman spectra, and (g) Ni 2p3/2 X-ray photoelectron spectroscopy (XPS) spectra of EG–NF and control samples (EG and NF). (Image: Reproduced from DOI:10.1016/j.eng.2024.04.028, CC BY) Characterization by scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS) confirmed the structural and chemical changes at the surface. In situ measurements further showed that the EG-mediated process suppressed beta-NiOOH formation and stabilized the more active gamma phase. During the reduction step of the process, single nickel atoms and small clusters became anchored onto the graphene layers, creating extra catalytic sites. The graphene coating also shielded the underlying metallic nickel from excessive oxidation, preserving the electrode’s structural integrity. The resulting EG-modified nickel foam electrode (EG-NF) delivered a lower overpotential at benchmark current density and a smaller Tafel slope than unmodified nickel foam, indicating faster OER kinetics. Electrochemical impedance spectroscopy confirmed that charge transfer resistance decreased, while the electrochemically active surface area increased — both factors contributing to the performance gains. To test the generality of the strategy, the team varied the type of graphene used and applied the same approach to other nickel-based substrates. When they coated a nickel-iron (NiFe) bimetallic system with optimized graphene layers, the resulting EG-NiFe electrode achieved even better OER metrics. Long-term durability tests demonstrated stable operation at high current density over extended periods, a critical requirement for industrial alkaline water electrolyzers. Density functional theory (DFT) calculations provided a mechanistic explanation for the experimental results. The simulations showed that gamma-NiOOH presents more thermodynamically favorable energetics for OER intermediate species compared to beta-NiOOH. Specifically, the calculated overpotential for the rate-determining step was lower on gamma-NiOOH surfaces, consistent with the measured performance gains. By tuning which NiOOH phase forms during operation, the graphene-mediated interfacial redox approach offers a practical route to more efficient OER electrodes for sustainable hydrogen production through water splitting. The same principle could extend to other transition metal systems used in energy conversion applications, broadening its relevance beyond nickel-based catalysts.