Oxygen reduction reaction (ORR) is the heart of many new energy conversions and storage devices, such as metal-air batteries and fuel cells. However, ORR is currently facing the dilemma of sluggish intrinsic kinetics and the noble electrocatalysts of high price and low reserves. In this work, isolated Co atoms anchored on defective nitrogen-doped carbon graphene single-atom catalyst (Co-SAC/NC) are synthesized via the proposed movable type printing method. The prepared Co-SAC/NC catalyst demonstrates admirable ORR performance, with a high half-wave potential of 0.884 V in alkaline electrolytes and outstanding durability. In addition, an assembled zinc–air battery with prepared Co-SAC/NC as air-cathode catalyst displays a high-peak power density of 179 mW cm⁻² and a high-specific capacity (757 mAh g⁻¹). Density functional theory calculations confirm that the true active sites of the prepared catalyst are Co-N₄ moieties, and further reveal a significantly electronic structure evolution of Co sites in the ORR process, in which the project density of states and local magnetic moment of Co atom varies during its whole reaction process. This work not only paves a new avenue for synthesizing SACs as robust electrocatalysts, but also provides an electronic-level insight into the evolution of the electronic structure of single-atom catalysts.

The oxygen evolution reaction (OER) represents an anodic reaction for a variety of sustainable energy conversion and storage technologies, such as hydrogen production, CO₂ reduction, etc. To realize the large-scale implementation of these technologies, the sluggish kinetics of the OER resulting from multi-step proton/electron transfer and occurring at the gas–liquid–solid triple-phase boundary needs to be accelerated. Manganese oxide-based (MnO_x) materials, especially MnO₂, have become promising non-precious metal electrocatalysts for the OER under acidic conditions due to the good trade-off between catalytic activity and stability. This paper reviews the recent progress of MnO₂-based materials to catalyze the OER through either the traditional adsorbent formation mechanism (AEM) or the emerging lattice-oxygen-mediated mechanism (LOM). Pure manganese dioxide OER catalysts with different crystalline structures and morphologies are summarized, while MnO₂-based composite structures are also discussed, and the application of MnO₂-based catalysts in PEMWEs is summarized. Critical challenges and future research directions are presented to hopefully help future research.

Recycling precious metals with high-efficiency is undoubtedly beneficial to optimize resource utilization for environmental remediation and sustainable development. Herein, we report an efficient route to recycle the palladium (Pd) and platinum (Pt) electrocatalysts using a phase transfer method. This strategy involves acidic dissolution of deactivated precious metal (Pd/Pt) electrocatalysts from their loading substrates, mixing with an ethanolic solution of dodecylamine (DDA), subsequent extraction of metal ions into a non-polar organic phase, and final reduction by sodium borohydride to reproduce high-performance electrocatalysts towards typical electrochemical reactions, e.g., oxygen reduction reaction (ORR) and ethanol oxidation reaction (EOR). In specific, the transfer efficiencies are up to 98% and the final recovery rate is over 85% for Pd and Pt electrocatalysts in each cycle. This approach symbolizes a facile and efficient way to recover precious metals, which might be applied to recycling a wide range of metals in various realms after appropriate modifications.