g-C3N4 promoted MOF-derived Fe single atoms anchored on N-doped hierarchically porous carbon for high-performance Zn-air batteries

In situ construction of MOF derived CoNC anchored on N-doped carbon xerogel sphere as efficient bifunctional ORR/OER electrocatalyst for Zn-air batteries

Electrocatalytic materials with dual functions of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) have received increasing attention in the field of zinc-air batteries (ZABs) research. In this study, bifunctional CoNC@NCXS catalysts were prepared by anchoring Co and N co-doped CoNC on N-doped carbon xerogel sphere (NCXS) based on the spatially confined domain effect and in-situ doping technique. CoNC@NCXS exhibited excellent ORR/OER activity in alkaline electrolytes with the ORR onset potential of 0.99 V, the half-wave potential (E1/2) of 0.78 V at 10 mA cm-2 and the OER overpotential of 360 mV at 10 mA cm-2. These excellent catalytic activities were derived from constructing composite active structures and enhancing electrocatalytic efficiency. The ZAB assembled with CoNC@NCXS catalyst had a discharge specific capacity of 710 mAh g-1 at a current density of 10 mA cm-2, which was superior to that of the Pt/C&RuO2 catalyst-assembled battery (667 mAh g-1). After running for 150 h, the charge and discharge efficiency of the CoNC@NCXS battery decreased by only 12.8%, which confirmed the excellent stability of the CoNC@NCXS catalyst. The free energy diagrams showed that, CoNC@NCXS has lower energy barriers and higher potential than CoNC in key reaction steps. This study provides a new perspective for the structural design of highly active composite catalysts in energy storage and conversion.

Recent Achievements in Heterogeneous Bimetallic Atomically Dispersed Catalysts for Zn-Air Batteries: A Minireview

Rechargeable Zn-air batteries (ZABs) hold promise as the next-generation energy-storage devices owing to their affordability, environmental friendliness, and safety. However, cathodic catalysts are easily inactivated in prolonged redox potential environments, resulting in inadequate energy efficiency and poor cycle stability. To address these challenges, anodic active sites require multiple-atom combinations, that is, ensembles of metals. Heterogeneous bimetallic atomically dispersed catalysts (HBADCs), consisting of heterogeneous isolated single atoms and atomic pairs, are expected to synergistically boost the cyclic oxygen reduction and evolution reactions of ZABs owing to their tuneable microenvironments. This minireview revisits recent achievements in HBADCs for ZABs. Coordination environment engineering and catalytic substrate structure optimization strategies are summarized to predict the innovation direction for HBADCs in ZAB performance enhancement. These HBADCs are divided into ferrous and nonferrous dual sites with unique microenvironments, including synergistic effects, ion modulation, electronic coupling, and catalytic activity. Finally, conclusions and perspectives relating to future challenges and potential opportunities are provided to optimise the performance of ZABs.

FeN4S1 Single-Atom Sites Anchored on Three-Dimensional Porous Carbon for Highly Efficient and Durable Oxygen Electrocatalysis

Precisely designing asymmetric active centers and exploring their electronic regulation effects to prepare efficient bifunctional single-atom catalysts (SACs) is important for boosting the practical applications of zinc-air batteries (ZABs). Herein, an effective strategy has been developed by introducing an axial S atom to the FeN4 active center, simultaneously assisted by pyrolyzing the graphene oxide (GO) sheathed zeolitic-imidazolate framework-8 (ZIF8) composite and constructing a three-dimensional (3D) porous framework with abundant FeN4S1 moieties. This structure can accelerate the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) kinetics owing to the modulated electronic redistribution and d-band center with a reduced energy barrier. The optimal S-Fe-NC/rGO showcases a lower voltage gap (ΔE) of 0.64 V between both the ORR and OER half-wave potentials at 10 mA cm-2, highlighting the excellent bifunctional activities. The assembled S-Fe-NC/rGO rechargeable liquid ZABs deliver a power density of 154.05 mW·cm-2 and a desirable durability of >900 h. More importantly, the corresponding flexible solid-state ZABs exhibit considerable foldability.

High-Performance Bifunctional Electrocatalysts for Flexible and Rechargeable Zn-Air Batteries: Recent Advances

Flexible rechargeable Zn-air batteries (FZABs) exhibit high energy density, ultra-thin, lightweight, green, and safe features, and are considered as one of the ideal power sources for flexible wearable electronics. However, the slow and high overpotential oxygen reaction at the air cathode has become one of the key factors restricting the development of FZABs. The improvement of activity and stability of bifunctional catalysts has become a top priority. At the same time, FZABs should maintain the battery performance under different bending and twisting conditions, and the design of the overall structure of FZABs is also important. Based on the understanding of the three typical configurations and working principles of FZABs, this work highlights two common strategies for applying bifunctional catalysts to FZABs: 1) powder-based flexible air cathode and 2) flexible self-supported air cathode. It summarizes the recent advances in bifunctional oxygen electrocatalysts and explores the various types of catalyst structures as well as the related mechanistic understanding. Based on the latest catalyst research advances, this paper introduces and discusses various structure modulation strategies and expects to guide the synthesis and preparation of efficient bifunctional catalysts. Finally, the current status and challenges of bifunctional catalyst research in FZABs are summarized.

Research Progress on Atomically Dispersed Fe-N-C Catalysts for the Oxygen Reduction Reaction

The efficiency and performance of proton exchange membrane fuel cells (PEMFCs) are primarily influenced by ORR electrocatalysts. In recent years, atomically dispersed metal-nitrogen-carbon (M-N-C) catalysts have gained significant attention due to their high active center density, high atomic utilization, and high activity. These catalysts are now considered the preferred alternative to traditional noble metal electrocatalysts. The unique properties of M-N-C catalysts are anticipated to enhance the energy conversion efficiency and lower the manufacturing cost of the entire system, thereby facilitating the commercialization and widespread application of fuel cell technology. This article initially delves into the origin of performance and degradation mechanisms of Fe-N-C catalysts from both experimental and theoretical perspectives. Building on this foundation, the focus shifts to strategies aimed at enhancing the activity and durability of atomically dispersed Fe-N-C catalysts. These strategies encompass the use of bimetallic atoms, atomic clusters, heteroatoms (B, S, and P), and morphology regulation to optimize catalytic active sites. This article concludes by detailing the current challenges and future prospects of atomically dispersed Fe-N-C catalysts.