摘要/Abstract

双金属氢氧化物(LDH)是催化析氧反应(OER)活性最佳的一类催化剂, 其中揭示双金属位点的协同作用是进一步提升其电催化、光催化性能的关键. 本工作采用密度泛函方法, 从理论计算角度探究了五种MN³⁺-LDH (M²⁺= Co²⁺、Ni²⁺, N³⁺=Al³⁺、Cr³⁺、Mn³⁺、Fe³⁺)在催化OER中的反应机制和双金属位点的协同作用. 研究结果表明, 在电催化OER中, 氧物种以桥连的方式同时吸附在双金属位点上, 双位点协同作用降低了OER中的电势决定步骤的自由能变, 并有效降低了电催化OER的过电位. Ni₃Fe-LDH在五种LDH中具有最高的电催化OER活性. 在光催化OER中, 双金属协同作用影响了LDH的带隙、功函数及驱动力, 进而决定了LDH光催化OER的能力. 所研究的五种LDH均为可见光响应, 其中Ni₃Cr-LDH由于其驱动力大于过电位而被预测为良好的OER光催化剂.
关键词: 双金属氢氧化物, 析氧反应, 协同作用, 催化机制, 理论计算
Layered double hydroxides (LDHs) has played an important role in the field of catalysis because of its high dispersion of active sites, adjustable layer elements, and exchangeable interlayer anions. LDHs show excellent catalytic activity in oxygen evolution reaction (OER), due to the specific synergistic effect of double metals site. Thus, it is crucial to reveal the role of synergistic effect for promoting catalytic performance of photocatalyst and electrocatalyst. Although great efforts from experimental workers have been devoted to exploring the types and ratios of bimetals in LDHs, the role of synergistic effect on OER is still unclear. In this work, we systematically investigated the synergistic mechanism and the role of synergistic effect on OER performances based on density functional theory calculation plus U (DFT+U) method. Five kinds of LDHs (MN³⁺-LDH (M²⁺=Co²⁺, Ni²⁺; N³⁺=Al³⁺, Cr³⁺, Mn³⁺, Fe³⁺)) were built to study the synergistic effect from different bimetal. The results showed that oxygen species is bridged by one M²⁺and one N³⁺metal, forming a stable adsorption structure. For electrocatalytic OER, the synergistic effect of the bimetallic sites decreased the free energy change of the potential-determining step, and further reduces the overpotential of the electrocatalytic oxygen evolution reaction. Therein, Ni₃Fe-LDH has the lowest overpotential, exhibiting superior electrocatalytic OER activity among the five LDHs. This is not the case in photocatalytic OER, the synergy of bimetals affects the band gap, work function and driving force of LDHs, which determine the ability of LDH photocatalytic OER. The five types of LDH studied are all visible light response, and Ni₃Cr-LDH is predicted to be a good OER photocatalyst in view of its higher driving force than the overpotential. This work reveals the synergistic effect of bimetal in LDH on OER activity from a micro-atomic level, which will provide theoretical insights for the design of novel LDH-based catalysts.
Key words: layered double hydroxide, oxygen evolution reaction, synergy, catalytic mechanism, theoretical calculation


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