Department of Materials Science and Engineering, College of Engineering, Peking University, Beijing, China.
BIC-ESAT, College of Engineering, Peking University, Beijing, China.
Nature. 2019 Oct;574(7776):81-85. doi: 10.1038/s41586-019-1603-7. Epub 2019 Sep 25.
The efficient interconversion of chemicals and electricity through electrocatalytic processes is central to many renewable-energy initiatives. The sluggish kinetics of the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) has long posed one of the biggest challenges in this field, and electrocatalysts based on expensive platinum-group metals are often required to improve the activity and durability of these reactions. The use of alloying, surface strain and optimized coordination environments has resulted in platinum-based nanocrystals that enable very high ORR activities in acidic media; however, improving the activity of this reaction in alkaline environments remains challenging because of the difficulty in achieving optimized oxygen binding strength on platinum-group metals in the presence of hydroxide. Here we show that PdMo bimetallene-a palladium-molybdenum alloy in the form of a highly curved and sub-nanometre-thick metal nanosheet-is an efficient and stable electrocatalyst for the ORR and the OER in alkaline electrolytes, and shows promising performance as a cathode in Zn-air and Li-air batteries. The thin-sheet structure of PdMo bimetallene enables a large electrochemically active surface area (138.7 square metres per gram of palladium) as well as high atomic utilization, resulting in a mass activity towards the ORR of 16.37 amperes per milligram of palladium at 0.9 volts versus the reversible hydrogen electrode in alkaline electrolytes. This mass activity is 78 times and 327 times higher than those of commercial Pt/C and Pd/C catalysts, respectively, and shows little decay after 30,000 potential cycles. Density functional theory calculations reveal that the alloying effect, the strain effect due to the curved geometry, and the quantum size effect due to the thinness of the sheets tune the electronic structure of the system for optimized oxygen binding. Given the properties and the structure-activity relationships of PdMo metallene, we suggest that other metallene materials could show great promise in energy electrocatalysis.
通过电催化过程实现化学物质和电能的高效转化是许多可再生能源计划的核心。氧还原反应（ORR）和氧析出反应（OER）的缓慢动力学一直是该领域面临的最大挑战之一，通常需要基于昂贵的铂族金属的电催化剂来提高这些反应的活性和耐久性。合金化、表面应变和优化的配位环境的使用导致了基于铂的纳米晶体，这些纳米晶体在酸性介质中具有非常高的 ORR 活性；然而，由于在存在氢氧化物的情况下难以在铂族金属上实现优化的氧结合强度，因此改善碱性环境中的该反应的活性仍然具有挑战性。在这里，我们表明 PdMo 双金属烯——一种高度弯曲的亚纳米厚金属纳米片形式的钯-钼合金——是一种在碱性电解质中高效且稳定的 ORR 和 OER 电催化剂，并在 Zn-空气和 Li-空气电池中作为阴极表现出有前景的性能。PdMo 双金属烯的薄片状结构使它具有较大的电化学活性表面积（每克钯 138.7 平方米）和高原子利用率，导致碱性电解质中相对于可逆氢电极的 ORR 质量活性为 16.37 安培每毫克钯在 0.9 伏时。这种质量活性分别比商业 Pt/C 和 Pd/C 催化剂高 78 倍和 327 倍，在 30000 个电位循环后几乎没有衰减。密度泛函理论计算表明，合金化效应、由于弯曲几何形状引起的应变效应以及由于薄片的薄度引起的量子尺寸效应调谐了系统的电子结构以实现优化的氧结合。鉴于 PdMo 金属烯的性质和结构-活性关系，我们建议其他金属烯材料在能源电催化方面可能具有很大的潜力。
