The exploration of earth-abundant electrocatalysts with high performance for the oxygen evolution reaction (OER) is eminently desirable and remains a significant challenge. The composite of the metal-organic framework (MOF) Ni₁₀Co-BTC (BTC = 1,3,5-benzenetricarboxylate) and the highly conductive carbon material ketjenblack (KB) could be easily obtained from the MOF synthesis in the presence of KB in a one-step solvothermal reaction. The composite and the pristine MOF perform better than commercially available Ni/NiO nanoparticles under the same conditions for the OER. Activation of the nickel-cobalt clusters from the MOF can be seen under the applied anodic potential, which steadily boosts the OER performance. Ni₁₀Co-BTC and Ni₁₀Co-BTC/KB are used as sacrificial agents and undergo structural changes during electrochemical measurements, the stabilized materials show good OER performances.

Asymmetric transition metal catalysts offer a path to energy devices such as water electrolysis and metal–air batteries based on non-precious metals. This work reviews strategies for their design, reaction mechanisms, and future challenges.

Efficient and durable catalysts for the oxygen evolution reaction (OER) are of great importance for energy storage and conversion devices. However, an objective evaluation and fair comparison of different catalysts remain challenging due to the different catalyst loadings and substrates for OER measurements. In this work, we investigated NiFe layer double hydroxide and commercial Ni/NiO catalysts with different loadings and substrates of glassy carbon (GC), porous nickel foam (NF), and carbon paper (CP). The activity, cycling stability, and potentiostatic stability of the catalysts are compared with respect to the loading and substrate. Catalyst loading exhibits a volcano trend with OER activity, while it has little impact on stability. The 3D substrates NF and CP significantly improved the OER activity of the catalysts compared to GC, especially at higher loadings. The consistent degradation trend of the catalysts confirms the validity of using NF or CP as substrates for the stability test.

Identifying active sites in FeNC catalysts for oxygen reduction reactions (ORR) and active site changes during preparation, storage, and electrochemical cycling are key challenges in the quest for improved catalysts. In this work, high-resolution transmission electron microscopy (TEM) is combined with ⁵⁷Fe Mössbauer and electron paramagnetic resonance (EPR) spectroscopies to investigate iron centers in high-performance FeNC catalysts with regard to their structure, coordination, and oxidation and spin states. Reversible and irreversible changes during storage, the preparation of FeNC electrodes, and their use in electrochemical cells are investigated by complementary spectroelectrochemical Mössbauer and EPR methods. Microscopy of the as-prepared FeNC materials reveals iron to be evenly distributed in isolated sites or a few atoms containing sites. Mössbauer and EPR identify weakly and strongly magnetically coupled high-spin Fe(III) in rhombically distorted octahedral coordination or superparamagnetic clusters, high-spin Fe(II) sixfold coordinated in iron oxides, and intermediate-spin Fe(II) in square planar coordination. Upon oxygen exposure, a notable oxidation state change from Fe(II) to Fe(III) is observed, the iron is less evenly distributed, and larger iron oxide nanoparticles are formed. It is noted that for this catalyst, before and after oxygen exposure, most of the iron is bound in iron oxide structures. Under the applied potential, Fe(III) is partially reduced to Fe(II) in clustered and isolated or weakly coupled sites. This change is mostly reversible, suggesting structural retention of the majority of the catalyst.

In this study, we present the facile formation of platinum nanoparticles (Pt-NPs) on reduced graphite oxide (rGO) (Pt-NP@rGO) by microwave-induced heating of the organometallic precursor ((MeCp)PtMe₃ in different tunable aryl alkyl ionic liquids (TAAIL). In the absence of rGO, transmission electron microscopy (TEM) reveals the formation of dense aggregates of Pt-NPs, with primary particle sizes of 2 to 6 nm. In contrast, in the Pt-NP@rGO samples, Pt-NPs are homogeneously distributed on the rGO, without any aggregation. Pt-NP@rGO samples are used as electrode materials for oxygen reduction reaction (ORR), which was assessed by cyclic voltammetry (CV) and linear sweep voltammetry (LSV). The electrochemical surface area (ECSA) and mass-specific activity (MA) increase up to twofold, compared with standard Pt/C 60%, making Pt-NP@rGO a competitive material for ORR.