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1. Electrochemical behavior of a Ni ₃ N OER precatalyst in Fe-purified alkaline media: the impact of self-oxidation and Fe incorporation

   https://doi.org/10.1039/D1MA00130B  

   Kawashima, Kenta; Márquez-Montes, Raúl A.; Li, Hao; Shin, Kihyun; Cao, Chi L.; Vo, Kobe M.; Son, Yoon Jun; Wygant, Bryan R.; Chunangad, Adithya; Youn, Duck Hyun; et al (April 2021, Materials Advances)

   null (Ed.)

   Nickel nitride (Ni 3 N) is known as one of the promising precatalysts for the electrochemical oxygen evolution reaction (OER) under alkaline conditions. Due to its relatively low oxidation resistance, Ni 3 N is electrochemically self-oxidized into nickel oxides/oxyhydroxides (electroactive sites) during the OER. However, we lack a full understanding of the effects of Ni 3 N self-oxidation and Fe impurity incorporation into Ni 3 N from electrolyte towards OER activity. Here, we report on our examination of the compositional and structural transformation of Ni 3 N precatalyst layers on Ni foams (Ni 3 N/Ni foam) during extended periods of OER testing in Fe-purified and unpurified KOH media using both a standard three-electrode cell and a flow cell, and discuss their electrocatalytic properties. After the OER tests in both KOH media, the Ni 3 N surfaces were converted into amorphous, nano-porous nickel oxide/(oxy)hydroxide surfaces. In the Fe-purified electrolyte, a decrease in OER activity was confirmed after the OER test because of the formation of pure NiOOH with low OER activity and electrical conductivity. Conversely, in the unpurified electrolyte, a continuous increase in OER activity was observed over the OER testing, which may have resulted from the Fe incorporation into the self-oxidation-formed NiOOH. Our experimental findings revealed that Fe impurities play an essential role in obtaining notable OER activity using the Ni 3 N precatalyst. Additionally, our Ni 3 N/Ni foam electrode exhibited a low OER overpotential of 262 mV to reach a geometric current density of 10 mA cm geo −2 in a flow cell with unpurified electrolyte. 

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2. Spectroelectrochemical Studies of Oxygen Evolution Reaction Kinetics for Surface-Incorporated Iron in Nickel Oxyhydroxide Electrocatalysts

   https://doi.org/10.1021/acscatal.5c09080  

   Wang, Yifeng; Twight, Liam P; Sagui, Nicole A; Kwak, Minkyoung; Boettcher, Shannon W; Moss, Benjamin S; Stephens, Ifan_E L; Durrant, James R; Rao, Reshma R (March 2026, ACS Catalysis)

   NixFe1−xOyHz is the state-of-the-art catalyst for the oxygen evolution reaction (OER) in alkaline water electrolyzers; however, understanding the impact of Fe on the active sites, reaction mechanism, and consequently intrinsic activity has been under intense debate. In this work, operando UV−vis spectroscopy was used to investigate Fe-free NiOxHy and NiOxHy with Fe selectively incorporated onto the surface. At oxygen-evolution potentials, similar oxidized nickel states were present before and after the Fe incorporation, with negligible changes in their redox potentials. However, the discharge kinetics of the Ni states show a substantial acceleration after the introduction of Fe, consistent with an increase in OER kinetics upon Fe incorporation and formation of active Ni−Fe species. Using optical spectroscopy, we determined the intrinsic reaction time constant per surface Fe site is <0.1 s, which is 2 orders of magnitude faster than Ni sites not in proximity to surface Fe sites (∼10 s), and also an order of magnitude faster than Ni sites in pure NiOxHy (∼1 s). Consequently, we propose that the OER occurs via charge accumulation primarily on Ni centers in these catalysts, followed by hole transport to the surface Fe species where oxygen evolution occurs. 

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3. Electrochemical Oxide Growth on Nickel and Commercial Nickel Alloys: Influence of Chromium and Molybdenum

   https://doi.org/10.1149/1945-7111/acd7a6  

   Kretzmer, Isaac; Stuve, Eric M. (June 2023, Journal of The Electrochemical Society)

   Nickel-chromium-molybdenum (NiCrMo) alloys are well-known for having exceptional corrosion resistance, but their electrocatalytic properties have not been extensively studied. In this paper, the development of electro-active nickel-oxyhydroxide (NiOOH) phases and kinetics of the oxygen evolution reaction (OER) have been examined on alloys G35, B3, and C276 in alkaline electrolyte at 25 °C. Reproducible oxide layers were grown by potential cycling between 0.85 and 1.52 V vs RHE up to 600 cycles, and the transition between Ni(OH) 2 and NiOOH was monitored by cyclic voltammetry throughout. Onset potentials, Tafel slopes, and turnover frequencies (TOF) were measured at OER overpotentials between 270 and 390 mV. Alloys with dissimilar Cr:Mo ratios had significantly higher electrochemical surface area and increased γ -NiOOH formation, suggesting higher metal dissolution rates. The equal Cr:Mo concentration alloy and pure Ni developed a primarily β -NiOOH surface, and had 1.8–2.0 times larger TOF values than those containing significant γ -NiOOH. The NiCrMo alloys required smaller overpotentials (54–80 mV) to produce 10 mA cm −2 of OER current, and had comparable Tafel slopes to pure Ni. The findings here indicate a β -NiOOH-developed surface to be more OER-active than a γ -NiOOH-developed surface, and suggest certain NiCrMo alloys have promise as OER electrocatalysts. 

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4. Tuning the intrinsic catalytic activities of oxygen-evolution catalysts by doping: a comprehensive review

   https://doi.org/10.1039/D1TA04032D  

   Ede, Sivasankara Rao; Luo, Zhiping (September 2021, Journal of Materials Chemistry A)

   null (Ed.)

   Electrochemical water splitting produces clean hydrogen fuel as one of the pivotal alternative energies to fossil fuels in the near future. However, the anodic oxygen evolution reaction (OER) is a significant bottleneck that curtails large-scale applications of electrochemical water splitting technology, owing to its sluggish reaction kinetics. In the past few decades, various methods have been proposed to improve the OER kinetics. Among them, doping is a simple and efficient method to mold the OER kinetics of a catalyst by incorporating different or hetero atoms into the host lattice. These efforts are vital to design highly efficient OER catalysts for real-world applications. However, the OER mechanism of a doped catalyst varies, depending on the host lattice and the dopant. This review highlights different doping strategies and associated OER mechanisms of state-of-the-art catalysts, including oxides (noble metal oxides, perovskite oxides, spinel oxides, hydroxides and others), non-oxides (metal sulfides, metal selenides, metal phosphides, metal nitrides and metal carbides), and carbon-based catalysts (graphene, carbon nanotubes and others). Fundamental understanding of the doping effects on the OER from combined experimental and theoretical research provides guidelines for designing efficient catalysts. 

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5. Lewis Acid Site Engineering in Chromite Spinels Orchestrated Surface Reconstruction and Surpasses RuO ₂ in Oxygen Evolution

   https://doi.org/10.1002/smll.202508245  

   Krishnan, Abhirami V; Saini, Kavish; Enriquez, Lissette Garcia; Ramana, C V; Sreenivasan, Sreeprasad T (November 2025, Small)

   Abstract Atomic‐scale engineering of chromite spinels featuring redox‐active tetrahedral A‐sites and strong Cr–O covalency offers a promising route to superior platinum‐group‐metal‐free oxygen evolution reaction (OER) catalysts. However, comprehensive studies addressing how cation substitution influences surface chemistry and governs OER activity and durability in chromite spinels remain limited. Here, a systematic investigation of the multicationic chromite series Ni_xFe_yCr_3−x−yO₄is presented, identifying composition‐dependent Lewis acidity as a descriptor of superior OER performance. It is further demonstrated that tuning surface acidity directly controls dynamic reconstruction processes and lattice‐oxygen participation during spinel‐based electrocatalysis. Following activation, the optimized Ni₀.₈Fe₀.₃Cr₁.₉O₄catalyst delivers a current density of 10 mA cm⁻²at an overpotential of 235 mV, surpassing RuO₂, with excellent long‐term stability. Integrating microscopic and spectroscopic analysis with operando impedance spectroscopy, it shows that activation generates an oxyhydroxide overlayer and reveals a previously unrecognized link between surface Lewis acidity and the growth kinetics and activity of these shells. Density functional theory calculations indicate that Fe incorporation at octahedral sites raises the O 2p‐band center and lowers oxygen‐vacancy formation energy, promoting lattice‐oxygen activation and triggering reconstruction, yielding enhanced OER. This work integrates cation‐driven surface‐acidity modulation, acidity‐governed reconstruction, and OER activity enhancement into a unified predictive framework for designing earth‐abundant spinel‐based catalysts. 

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