摘要
金属和氮共掺杂碳(M-N-Cs)由于具有高原子利用率、良好的活性和选择性,因而被认为是具有潜力的氧电催化剂.但其热力学氧化势较低,碳材料在高电位下容易腐蚀.在放电过程中,锌空气电池正极的电位始终比碳氧化的热力学电位高约0.5 V,这导致阴极中碳的严重腐蚀.对于M-N-C,腐蚀会破坏金属氮配位(M-Nx)活性位点,导致活性比表面积减少,同时还会改变孔隙形貌和表面特性,进而降低其催化活性.在充电(即氧气析出反应,OER)过程中,这种腐蚀现象会进一步加剧.因此,开发一种既具有高效双功能催化活性,又具有良好抗电化学腐蚀性能的M-N-C催化剂,对于解决上述问题至关重要.本文利用氮化碳(g-C_(3)N_(4))支撑钴氮配位(Co-Nx)活性位点,同时包覆科琴黑(KB)形成馄饨结构,制备了双功能氧催化剂KB@Co-C_(3)N_(4).首先,将剥离的C_(3)N_(4)与KB混合后煅烧,得到C_(3)N_(4)包覆的KB材料(KB@C_(3)N_(4));随后,再次煅烧将Co单原子引入KB@C_(3)N_(4)中,形成具有高活性和高稳定性的KB@Co-C_(3)N_(4)氧催化剂.红外光谱结果证实了,KB@Co-C_(3)N_(4)中存在C_(3)N_(4)成分.透射电镜和元素标记结果表明,C_(3)N_(4)均匀包覆在KB基底上.同步辐射测试确定了Co单原子的配位环境为CoN4结构.在0.5 mol L^(-1) NH_(4)Cl溶液中测试了KB@Co-C_(3)N_(4)氧催化剂ORR/OER的催化活性和稳定性.结果表明,KB@CoC_(3)N_(4)表现出较好的ORR性能,半波电位为0.723 V,显著优于商业铂碳催化剂(0.673 V)和普通Co-N-C催化剂(0.694 V).经过40000圈加速耐久性测试,KB@Co-C_(3)N_(4)仅衰减9 mV,而商业铂碳和Co-N-C在7500圈测试后分别衰减41和44 mV.在OER方面,KB@Co-C_(3)N_(4)在10 mA cm^(-2)时的过电位为550 mV,优于氧化钌的560 mV和Co-N-C的600 mV.经过20000圈测试,KB@Co-C_(3)N_(4)的OER过电位几乎保持不变,而氧化钌和Co-N-C经过4000圈测试后分别增加了37和20 mV.透射电镜观察发现,KB@Co-C_(3)N_(4)在实验前后形貌未发生明显变化,证明了其较好的稳定性.理论计算揭示,C_(3)N_(4)能够优化Co金属活性位点的电子结构,改善Co中心的电荷分布并增强Co-N键强度;同时,C_(3)N_(4)对KB基底的包覆有效避免了KB在高电位下的腐蚀,确保了KB@Co-C_(3)N_(4)的高稳定性和催化活性.将KB@Co-C_(3)N_(4)应用于中性锌空气电池中,该电池展现出1.52 V的开路电压,并在5 mA cm^(-2)的高电流密度下稳定循环运行超过985 h,性能优于大多数报道的采用碳基材料作为阴极催化剂的中性锌空气电池.综上所述,馄饨结构的KB@Co-C_(3)N_(4)具有较好的氧催化活性和稳定性,为设计高稳定性高活性的M-N-C催化剂提供了一定的参考.
This work addresses the challenges faced by oxygen catalysis applications in neutral media,which are hindered by sluggish kinetics and severe carbon corrosion.To overcome these issues,a bifunctional oxygen catalyst(KB@Co-C_(3)N_(4))was developed by utilizing graphitic carbon nitride(g-C_(3)N_(4))to support Co-Nx active sites and simultaneously to wrap Ketjen black(KB)to form a wonton structure.The resulting catalyst exhibited excellent ORR/OER activity and good stability in neutral electrolytes.The KB@Co-C_(3)N_(4) catalyst demonstrated a half-wave potential(E_(1/2))of 0.723 V and only a 9 mV decay after 40000 cycles of ORR accelerated durability test(ADT).In terms of OER,the overpotential at 10 mA cm–2(η10)of KB@Co-C_(3)N_(4) was 550 mV,with negligible increase observed even after 20 k cycles of OER ADT.The zinc-air battery incorporating KB@Co-C_(3)N_(4) exhibited superior performances over other benchmark bifunctional counterparts in open-circuit voltage(1.52 V),galvanostatic discharge/charge performance and cycling duration(985 h at 5 mA cm–2).The theoretical investigation revealed that the engineered electronic structures of the metal active sites enable precise regulation of the charge distribution of Co centers,leading to optimized adsorption and desorption of oxygenated intermediates.The high stability of the catalyst is attributed to the chemically stable C_(3)N_(4),which strengthens Co-Nx active sites and protects KB against carbon corrosion by wrapping KB to form the wonton structure.
作者
吴维凡
范晋歌
赵振宏
潘建敏
杨静
阎兴斌
詹怡
Wei-Fan Wu;Jin-Ge Fan;Zhen-Hong Zhao;Jian-Min Pan;Jing Yang;Xingbin Yan;Yi Zhan(School of Chemical Engineering and Technology,Sun Yat‐sen University,Zhuhai 519082,Guangdong,China;The Key Lab of Low‐Carbon Chemistry&Energy Conservation of Guangdong Province,Sun Yat‐sen University,Guangzhou 510275,Guangdong,China;State Key Laboratory of Optoelectronic Materials and Technologies,Department of Materials Science and Engineering,Sun Yat‐sen University,Guangzhou 510275,Guangdong,China)
基金
广东省基础与应用基础研究基金(2023A1515010134)。
关键词
氧电催化
单原子催化剂
中性电解液
抗腐蚀
Oxygen electrocatalysis
Single-atomic catalysts
Neutral electrolyte
Corrosion resistance
