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Aimed at developing a highly active and stable non-precious metal catalyst (NPMC) for oxygen reduction reaction (ORR) in acidic proton-exchange membrane fuel cells (PEMFCs), a novel NPMC was prepared by pyrolyzing a composite of carbon-supported Fe-doped graphitic carbon nitride (Fe−g-C 3 N 4 @C) above 700 °C. In this paper, the influence of the pyrolysis temperature and Fe content on ORR performance was investigated. Rotating disk electrode (RDE) and rotating ring-disk electrode (RRDE) studies reveal that, with a half-wave potential of 0.75 V [versus reversible hydrogen electrode (RHE)] and a H 2 O 2 yield of 2.6% at 0.4 V, the as-synthesized catalyst heat-treated at 750 °C with a Fe salt/dicyandiamide (DCD) mass ratio of 10% displays the optimal ORR activity and selectivity. Furthermore, the pyrolyzed Fe−N−C composite exhibits superior durability in comparison to that of commercial 20 wt % Pt/C in acidic medium, making it a good candidate for an ORR electrocatalyst in PEMFCs. KEYWORDS: non-precious metal catalyst (NPMC), oxygen reduction reaction (ORR), proton-exchange membrane fuel cell (PEMFC), carbon-supported Fe-doped g-C 3 N 4 (Fe−g-C 3 N 4 @C), pyrolysis, Fe−N−C composite

The world's mounting demands for environmentally benign and efficient resource utilization have spurred investigations into intrinsically green and safe energy storage systems. As one of the most promising types of batteries, the Zn battery family, with a long research history in the human electrochemical power supply, has been revived and reevaluated in recent years. Although Zn anodes still lack mature and reliable solutions to support the satisfactory cyclability required for the current versatile applications, many new concepts with optimized Zn/Zn 2+ redox processes have inspired new hopes for rechargeable Zn batteries. In this review, we present a critical overview of the latest advances that could have a pivotal role in addressing the bottlenecks (e.g., nonuniform deposition, parasitic side reactions) encountered with Zn anodes, especially at the electrolyte-electrode interface. The focus is on research activities towards electrolyte modulation, artificial interphase engineering, and electrode structure design. Moreover, challenges and perspectives of rechargeable Zn batteries for further development in electrochemical energy storage applications are discussed. The reviewed surface/interface issues also provide lessons for the research of other multivalent battery chemistries with low-efficiency plating and stripping of the metal.

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Conventional carbonate solvents with lowH OMO levels are theoretically compatible with the low-cost, highvoltage chemistry of Zn/graphite batteries.H owever,t he nucleophilic attacko ft he anion on carbonates induces an oxidative breakdown at high potentials.H ere,w er estore the inherent anodic stability of carbonate electrolytes by designing amicro-heterogeneous anion solvation network. Based on the addition of as trongly electron-donating solvent, trimethyl phosphate (TMP), the oxidation-vulnerable anion-carbonate affinities are decoupled because of the preferential sequestration of anions into solvating TMP domains around the metal cations.The hybridized electrolytes elevate the electrochemical window of carbonate electrolytes by 0.45 Va nd enable the operation of Zn/graphite dual-ion cells at 2.80 Vw ith al ong cycle life (92 %c apacity retention after 1000 cycles). By inheriting the non-flammability from TMP and the high iontransport kinetics from the carbonate systems,t his facile strategy provides cells with the additional benefits of fire retardancy and high-power capability.

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