Abstract:

Mo₂C/Mo₃P heterojunction was successfully anchored on porous defect-rich carbon substrate by using ZIF-8 as substrate and introducing metal Mo in situ into its framework structure and undergoing a high-temperature calcination treatment. Mo₂C/Mo₃P@NC exhibited a large specific surface area and sufficient active sites, and more important, it induced the transition of Mo to the low-valence state (Mo ^δ+, 0<δ<4), and the enhanced localized charge sites Mo ^δ+ significantly increased the defects and active sites. Moreover, the bivalent Mo ^δ+-Mo⁶⁺ sites constructed a favorable pathway for CO₂ adsorption-desorption, and lithium-ion and electron migration, stabilized the two-electron product Li₂C₂O₄ and prevented the disproportionation to four-electron product Li₂CO₃ during CORR process. The excellent catalytic properties of Mo₂C/Mo₃P@NC drive the lithium-carbon dioxide batteries to follow the two-electron reaction pathway (2Li⁺+2CO₂+2e^-→Li₂C₂O₄), greatly reducing the charging potential and the battery polarization. Li-CO₂ battery assembled with Mo₂C/Mo₃P@NC cathode achieved a full discharge capacity up to 10538mAh/g, a reversible charge capacity of 10521mAh/g, and an improved coulombic efficiency of 99.8%; and the potential difference between charge and discharge at a current density of 100mA/g is only 0.7V, with a small potential gap in a 1100h cycle.

Key words: Li-CO₂ battery, Mo₂C/Mo₃P, heterojunction, CO₂ reduction reaction

摘要：

以ZIF-8为基底并在其框架结构中原位引入金属Mo，进行高温煅烧处理，成功得到多孔富缺陷碳基底耦合的Mo₂C和Mo₃P异质结(Mo₂C/Mo₃P@NC)催化剂，Mo₂C/Mo₃P@NC呈现出较大的比表面积和充分的活性位点，更重要的是诱导Mo向低价态δ（0<δ<4）过渡，改变材料表面电荷分布，增强的局域电荷位点Mo ^δ+显著增加缺陷和活性位点，双价态Mo ^δ+-Mo⁶⁺位点构建出有利于CO₂吸-脱附，锂离子及电子迁移输运路径，在CO₂RR过程中稳定两电子产物Li₂C₂O₄，并防止歧化成四电子产物Li₂CO₃。Mo₂C/Mo₃P@NC优异的催化特性驱动锂-二氧化碳电池遵循两电子反应路径（2Li⁺+2CO₂+2e^-→Li₂C₂O₄），电池充电电位和极化情况显著缓解，全放电容量高达10538mAh/g，可逆充电容量为10521mAh/g，库仑效率提升到99.8%；在电流密度为100mA/g下充电-放电电位差仅为0.7V，能以较小的电位差稳定循环1100h。

关键词: 锂-二氧化碳电池, Mo₂C/Mo₃P催化剂, 异质结, 二氧化碳还原