Key Takeaways & Executive Findings
- •• • Co-BCN-950 achieves a peak power density of 216 mW cm-2 in zinc-air batteries, surpassing commercial Pt/C (151 mW cm-2) by 43%, directly addressing the power output limitation that hinders ZAB commercialization. • • The catalyst exhibits an open-circuit voltage of 1.43 V and a specific capacity of 790 mAh g-1, metrics that exceed typical Pt/C-based ZABs and indicate potential for high-energy-density applications. • • Asymmetric Co-N3B-O coordination mitigates scaling-relation constraints among ORR intermediates, as evidenced by the enhanced kinetics and stabilization of *OOH via hydrogen bonding, which is critical for reducing overpotentials in practical devices. • • The mild annealing synthesis route avoids Fenton-like reactions associated with Fe-N-C catalysts, offering a chemically robust alternative that could extend operational lifetime in rechargeable ZABs, though long-term degradation rates require further quantification.
Abstract
The commercial viability of zinc-air batteries (ZABs) is constrained by the sluggish kinetics of the oxygen reduction reaction (ORR), which necessitates robust, cost-effective catalysts. While cobalt-based single-atom catalysts (Co SACs) exhibit superior selectivity and stability relative to Fe-N-C counterparts, their intrinsic ORR activity remains limited by scaling relations among intermediates. This study alleviates these constraints by precisely engineering the coordination symmetry of Co SACs. Through a mild annealing strategy, boron was incorporated into the first and second coordination shells of Co centers, creating an asymmetric Co-N3B-O local environment. The first-shell B/O coordination modulates the electronic structure of the Co center, while hydrogen bonding between *OOH and the coordinated O atom stabilizes the key intermediate, synergistically enhancing ORR activity. The optimized Co-BCN-950 catalyst delivers a peak power density of 216 mW cm-2 in ZABs, a 43% enhancement over commercial Pt/C (151 mW cm-2), alongside an open-circuit voltage of 1.43 V and a specific capacity of 790 mAh g-1. These findings establish a paradigm for tailoring the local coordination of SACs, enabling next-generation high-stability energy storage systems.
1. Introduction
The sluggish kinetics of the cathodic oxygen reduction reaction (ORR) impose severe overpotentials that restrict the practical power output and energy efficiency of zinc-air batteries (ZABs). Although commercial platinum-on-carbon (Pt/C) catalysts exhibit exceptional ORR activity, their prohibitive cost, susceptibility to poisoning, and vulnerability to deactivation fundamentally impede widespread commercialization. Among non-precious metal alternatives, carbon-supported single-atom catalysts (SACs) have emerged as promising candidates due to maximized atomic utilization and tunable electronic structures. However, Fe-N-C SACs, despite intrinsic activities rivaling Pt/C, catalyze Fenton-like reactions with peroxide byproducts, generating aggressive radicals that compromise long-term operational stability. Cobalt-based single-atom catalysts (Co SACs) are less prone to such side reactions, offering improved chemical robustness, but conventionally feature symmetric Co-N4 coordination that leads to suboptimal adsorption and activation of oxygen intermediates, limiting four-electron ORR kinetics.
This study addresses the geometric and electronic limitations of symmetric Co-N4 sites by precisely engineering the coordination symmetry of Co SACs. Through a novel mild annealing strategy, boron is incorporated into the first and second coordination shells of Co centers, constructing an asymmetric Co-N3B-O local environment. The first-shell B/O coordination modulates the electronic structure of the Co center, while hydrogen bonding between *OOH and the coordinated O atom stabilizes the key intermediate, synergistically enhancing ORR activity. The resulting Co-BCN-950 catalyst delivers a peak power density of 216 mW cm-2 in ZABs, a 43% enhancement over commercial Pt/C (151 mW cm-2), along with an open-circuit voltage of 1.43 V and a specific capacity of 790 mAh g-1. These findings provide a compelling paradigm for tailoring the local coordination of SACs, paving the way for next-generation high-stability energy storage systems.
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Jize Li, Xudong Peng, Renyi Li, Jiaye Li, Wenchao Hu, Hsingkai Chu, Ruiqin Zhong, Xiao Hai (2026). Precision design of asymmetric cobalt single-atom catalysts for high-performance zinc-air batteries. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-026-4362-y
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Frequently Asked Questions
What is the long-term stability of Co-BCN-950 under continuous cycling in zinc-air batteries, and how does it compare to Pt/C?
The provided text does not specify degradation rates or cycle life. However, the abstract claims exceptional stability, and the introduction notes that Co SACs are less prone to Fenton-like reactions than Fe-N-C, suggesting improved robustness. Quantitative stability data (e.g., voltage loss over 1000 cycles) are not included in the extracted sections.
How does the cost of Co-BCN-950 compare to commercial Pt/C on a per-gram or per-kilowatt basis?
The text does not provide cost analysis. While Co is earth-abundant and cheaper than Pt, the synthesis involves boron incorporation and mild annealing, which may add processing costs. A detailed techno-economic assessment is required for parity evaluation.
What are the failure mechanisms of Co-BCN-950 under high-current-density operation or in the presence of impurities?
The text does not address failure mechanisms. Potential degradation pathways include demetalation of Co sites, boron leaching, or carbon corrosion. The asymmetric Co-N3B-O environment may enhance stability, but empirical stress tests are not reported in the provided sections.
Can the synthesis of Co-BCN-950 be scaled up for industrial production, and what are the critical process parameters?
The mild annealing strategy is described as novel, but scalability is not discussed. Key parameters such as annealing temperature (950°C implied by name), atmosphere, and boron precursor loading would require optimization for large-scale manufacturing. No yield or batch-to-batch consistency data are provided.
What is the specific role of boron in the second coordination shell, and how does it compare to other heteroatom dopants like phosphorus or sulfur?
The text states that boron in the first and second shells modulates the electronic structure and stabilizes *OOH via hydrogen bonding. Comparative studies with other dopants are not included. The asymmetric Co-N3B-O motif is unique, but its performance relative to Co-N3P or Co-N3S is not evaluated in the extracted sections.
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