Search

Given the unique characteristic of integrating CO2 conversion and renewable energy storage, metal–CO2 batteries (MCBs) are expected to become the next‐generation technology to address both environmental and energy crises. As involving complex gas–liquid–solid three‐phase interfacial reactions, cathodes of MCBs can significantly affect the overall battery operation, thus attracting much research attention. Compared to conventional materials, 2D materials offer great opportunities for the design and preparation of high‐performance catalyst cathodes, especially showing superior bifunctional electrocatalytic capacity for rechargeable MCBs. The inherent high‐specific‐surface area and diverse structural architectures of 2D materials enable their flexible and rational engineering designs toward kinetically favorable metal–CO2 electrochemistry. Herein this review, the cutting‐edge progresses of 2D materials‐based catalyst cathodes are presented in MCBs. The reaction mechanisms of various MCBs, including both nonaqueous and aqueous systems, are systematically introduced. Then, the design criteria of catalyst cathodes, and the merits and demerits of 2D materials‐based catalyst cathodes are discussed. After that, three representative engineering strategies (i.e., defect control, phase engineering, and heterostructure design) of 2D materials for high‐performance MCBs are systematically described. Finally, the current research advances are briefly summarized and the confronting challenges and opportunities for future development of advanced MCB cathodes are proposed.

Zinc-nitrate batteries can integrate energy supply, ammonia electrosynthesis, and sewage disposal into one electrochemical device. However, current zinc-nitrate batteries still severely suffer from the limited energy density and poor rechargeability. Here, we report the synthesis of tetraphenylporphyrin (tpp)-modified heterophase (amorphous/crystalline) rhodium-copper alloy metallenes (RhCu M-tpp). Using RhCu M-tpp as a bifunctional catalyst for nitrate reduction reaction (NO3RR) and ethanol oxidation reaction in neutral solution, a highly rechargeable and low-overpotential zinc-nitrate/ethanol battery is successfully constructed, which exhibits outstanding energy density of 117364.6 Wh kg-1 cat, superior rate capability, excellent cycling stability of ~400 cycles, and potential ammonium acetate production. Ex/in situ experimental studies and theoretical calculations reveal that there is a molecule-metal relay catalysis in NO3RR over RhCu M-tpp that significantly facilitates the ammonia selectivity and reaction kinetics via a low energy barrier pathway. This work provides an effective design strategy of multifunctional metal-based catalysts toward the high-performance zinc-based hybrid energy systems. [ABSTRACT FROM AUTHOR]

Electrochemical nitrate reduction reaction (NO3RR) to ammonia has been regarded as a promising strategy to balance the global nitrogen cycle. However, it still suffers from poor Faradaic efficiency (FE) and limited yield rate for ammonia production on heterogeneous electrocatalysts, especially in neutral solutions. Herein, we report one-pot synthesis of ultrathin nanosheet-assembled RuFe nanoflowers with low-coordinated Ru sites to enhance NO3RR performances in neutral electrolyte. Significantly, RuFe nanoflowers exhibit outstanding ammonia FE of 92.9% and yield rate of 38.68 mg h-1mgcat-1 (64.47 mg h-1 mgRu-1) at -0.30 and -0.65 V (vs. reversible hydrogen electrode), respectively. Experimental studies and theoretical calculations reveal that RuFe nan-oflowers with low-coordinated Ru sites are highly electroactive with an increased d-band center to guarantee efficient electron transfer, leading to low energy barriers of nitrate reduction. The demonstration of rechargeable zinc-nitrate batteries with large-specific capacity using RuFe nanoflowers indicates their great potential in next-generation electrochemical energy systems. [ABSTRACT FROM AUTHOR]