Electrocatalytic water splitting is limited by kinetics-sluggish oxygen evolution, in which the activity of catalysts depends on their electronic structure. However, the influence of electron spin polarization on catalytic activity is ambiguous. Herein, we successfully regulate the spin polarization of Co₃O₄ catalysts by tuning the concentration of cobalt defects from 0.8 to 14.5%. X-ray absorption spectroscopy spectra and density functional theory calculations confirm that the spin polarization of Co₃O₄ is positively correlated with the concentration of cobalt defects. Importantly, the enhanced spin polarization can increase hydroxyl group absorption to significantly decrease the Gibbs free energy change value of the OER rate-determining step and regulate the spin polarization of oxygen species through a spin electron-exchange process to easily produce triplet-state O₂, which can obviously increase electrocatalytic OER activity. In specific, Co₃O₄-50 with 14.5% cobalt defects exhibits the highest spin polarization and shows the best normalized OER activity. This work provides an important strategy to increase the water splitting activity of electrocatalysts via the rational regulation of electron spin polarization.

Tuning metal–support interactions (MSIs) is an important strategy in heterogeneous catalysis to realize the desirable metal dispersion and redox ability of metal catalysts. Herein, we use pre-reduced Co₃O₄ nanowires (Co-NWs) in situ grown on monolithic Ni foam substrates to support Ag catalysts (Ag/Co-NW-R) for soot combustion. The macroporous structure of Ni foam with crossed Co₃O₄ nanowires remarkably increases the soot–catalyst contact efficiency. Our characterization results demonstrate that Ag species exist as Ag⁰ because of the equation Ag⁺  + Co²⁺  = Ag⁰ + Co³⁺, and the pre-reduction treatment enhances interactions between Ag and Co₃O₄. The number of active oxygen species on the Ag-loaded catalysts is approximately twice that on the supports, demonstrating the significant role of Ag sites in generating active oxygen species. Additionally, the strengthened MSI on Ag/Co-NW-R further improves this number by increasing metal dispersion and the intrinsic activity determined by the turnover frequency of these oxygen species for soot oxidation compared with the catalyst without pre-reduction of Co-NW (Ag/Co-NW). In addition to high activity, Ag/Co-NW-R exhibits high catalytic stability and water resistance. The strategy used in this work might be applicable in related catalytic systems.

Br₂/Br⁻ is a promising redox couple in flow batteries because of its high potential, solubility, and low cost. However, the reaction between Br⁻ and Br₂ only involves a single-electron transfer process, which limits its energy density. Herein, a novel two-electron transfer reaction based on Br⁻/Br⁺ was studied and realized through Br⁺ intercalation into graphite to form a bromine–graphite intercalation compound (Br–GIC). Compared with the pristine Br⁻/Br₂ redox pair, the redox potential of Br intercalation/deintercalation in graphite is 0.5 V higher, which has the potential to substantially increase the energy density. Different from Br₂/Br⁻ in the electrolyte, the diffusion rate of Br intercalation in graphite decreases with increasing charge state because of the decreasing intercalation sites in graphite, and the integrity of the graphite structure is important for the intercalation reaction. As a result, the battery can continuously run for more than 300 cycles with a Coulombic efficiency exceeding 97% and an energy efficiency of approximately 80% at 30 mA/cm², and the energy density increases by 65% compared with Br⁻/Br₂. Combined with double-electron transfer and a highly reversible electrochemical process, the Br intercalation redox couple demonstrates very promising prospects for stationary energy storage.

Manganese oxides are a promising class of electrocatalysts for renewable energy devices, such as fuel cells. Mn(III) ions with e _g electron filling of − 1 are the active sites for manganese-based electrocatalysts. However, Mn(III) sites may be disproportionated during electrochemical reactions, thus reducing the number of Mn(III) active sites and decreasing the catalytic activity of manganese oxides. In this work, we developed a facile cyclic voltammetry method to monitor the evolution of Mn(III) sites on a series of manganese oxides under “working” conditions. We proposed a descriptor S _Mn(III) to describe the stability of Mn(III). Our simulated and experimental results show that the higher is S _Mn(III), the higher the active Mn(III) density, and the higher the electrocatalytic activity of the manganese oxide electrocatalyst.

Catalytic/initiated cracking of endothermic hydrocarbon fuels is an effective technology for cooling a hypersonic aircraft with a high Mach number (over 5). Catalysts and initiators can promote fuel cracking at low temperatures, increase fuel conversion and the heat sink capacity, and suppress coke deposition, thereby reducing waste heat. Catalysts mainly include metal oxide catalysts, noble metal catalysts and metal nanoparticles, zeolite catalysts, nanozeolite catalysts, and coating catalysts. Moreover, initiators roughly include nitrogenous compounds, oxygenated compounds, and hyperbranched polymer initiators. In this review, we aim to summarize the catalysts and initiators for cracking endothermic hydrocarbon fuels and their mechanisms for promoting cracking. This review will facilitate the development of the synthesis and exploration of catalysts and initiators.

Photocatalytic water splitting and carbon dioxide photoreduction are considered effective strategies for alleviating the energy crisis and environmental pollution. Polynuclear metal-oxo clusters possess excellent electron storage/release ability and unique catalytic properties via intermetallic synergy, which enables them with great potential in environmentally friendly photosynthesis. Importantly, metal-oxo clusters with precise structure can not only act as high-efficiency catalysts but also provide well-defined structural models for exploring structure–activity relationships. In this review, we systematically summarize recent progress in the catalytic application of polynuclear metal-oxo clusters, including polyoxometalate clusters, low-cost transition metal clusters, and metal-oxo-cluster-based metal–organic frameworks for water splitting and CO₂ reduction. Furthermore, we discuss the challenges and solutions to the problems of polynuclear metal-oxo clusters in photocatalysis.