Enhancing hydrogen evolution activity by doping and tuning the curvature of manganese-embedded carbon nanotubes
Enhancing hydrogen evolution activity by doping and tuning the curvature of manganese-embedded carbon nanotubes
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通过掺杂和调整嵌入锰的碳纳米管的曲率来增强析氢活性
DOI：
10.1039/c9cy01174a
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发表时间：
2019-10-07
影响因子：
5
通讯作者：
Guo, Wenyue
中科院分区：
文献类型：
--
作者：
Liu, Haijun;Zhao, Lianming;Guo, Wenyue
碳纳米管(CNTs)掺杂过渡金属在酸性电解液中的电催化析氢反应(HER)中具有很大的潜力。进一步阐明决定HER活性的潜在机制将有助于设计更高效的CNT基HER催化剂。本文采用第一性原理密度泛函理论方法，研究了一系列碳纳米管(MnCNT(n，n)S，n=3，4，5，6，7，9)与Mn和双N(MnN2CNT(5，5))共嵌的HER。理论计算表明，所有碳纳米管催化剂上的HER活性中心主要是金属中心附近的C原子，HER主要受Volmer-Heyrovsky机理支配，Heyrovsky反应为速率控制步骤。调节碳纳米管的曲率和嵌入杂原子(Mn和N)可以提高Cp带中心(epsilon(P))，削弱绝对H吸附自由能(|Delta G(H*)|)，降低绝对电极电位(Uabb0)，从而提高HER的性能。对于MnCNT(n，n)S来说，Her的活性与表面曲率有关，在n=5时达到峰值。在MnCNT(5，5)中掺入双N原子可以进一步提高Her的活性，表现为其电流密度是铂的30倍。此外，除了ΔG(H*)和自由能垒外，Uab0描述符还可以克服epsilon(P)适用于相同金属包埋碳纳米管的限制，从而扩展到描述过渡金属包埋碳纳米管体系的HER活性。
Carbon nanotubes (CNTs) incorporated with transition metals have been experimentally found to have great potential in the electrocatalytic hydrogen evolution reaction (HER) in acidic electrolytes. Further elucidating the underlying mechanism determining the HER activity will be helpful to design more highly efficient CNT-based catalysts for the HER. In this work, first-principles density functional theory calculations were performed to investigate the HER on a series of CNTs, substitutionally embedded with atomic Mn (MnCNT(n,n)s, n = 3, 4, 5, 6, 7, and 9) and co-embedded with Mn and double N (MnN2CNT(5,5)). The theoretical calculations suggest that the principal HER active sites on all studied CNT catalysts are the C atoms adjacent to the metal center, and the HER is dominated by the Volmer-Heyrovsky mechanism with the Heyrovsky reaction as the rate-determining step. Tuning the CNT curvatures and embedding heteroatoms (Mn and N) could elevate the C p-band center (epsilon(p)), weaken the absolute H adsorption free energy (|Delta G(H*)|), lower the absolute electrode potential (Uabs0), and thus enhance the HER performance. For MnCNT(n,n)s, the HER activity shows a volcano dependence on the surface curvature, peaking at n = 5. Substitutionally doping double N atoms into MnCNT(5,5) could further substantially enhance the HER activity, reflected by its thirtyfold current density relative to platinum. Furthermore, the Uabs0 descriptor, besides Delta G(H*) and the free energy barrier, could overcome the limitation of epsilon(p) applied in the same metal-embedded CNTs, extending to describe the HER activity of the transition metal-incorporated CNT system.