Enhancing the Alkaline Hydrogen Evolution Reaction Activity through the Bifunctionality of Ni(OH)2/Metal Catalysts
Enhancing the Alkaline Hydrogen Evolution Reaction Activity through the Bifunctionality of Ni(OH)2/Metal Catalysts
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DOI：
10.1002/anie.201204842
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发表时间：
2012-01-01
影响因子：
16.6
通讯作者：
Markovic, Nenad M.
中科院分区：
文献类型：
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作者：
Danilovic, N.;Subbaraman, Ram;Markovic, Nenad M.
析氢反应 (HER) 在许多重要技术领域发挥着关键作用，例如水和氯碱电解、[1] 金属沉积、[2] 腐蚀、[3] 以及二氧化碳还原生产燃料。 [4] HER 也具有根本重要性，数十年来一直作为模型反应来探索电极材料与质子（酸性）或水（碱性）电化学转化为分子氢 (2 H+[2 H2O]+ 2eÀ QH2+[2 OHÀ]) 的动力学速率之间的关系。[5]传统上，HER 的机理通常被认为是通过氢中间体（以下表示为 Had）的初始形成进行的，根据溶液的 pH 值，氢中间体是通过质子或水放电的电子转移步骤形成的 (H+[H2O]+ eÀ QHad-[+ OHÀ])。这个所谓的 Volmer 步骤之后是 Tafel 化学重组步骤 (2HadQH2) 或通过 Heyrovsky 步骤进行第二次电子转移 (H+[H2O]+ Had+ eÀ QH2 [+ OHÀ])。尽管由于活化水离解步骤，反应途径相似，但大多数催化剂在碱性介质中的 HER 活性通常比在酸性溶液中低约两到三个数量级。[5b, 6] 这种认识引发了 Ni (OH) 2/Pt 催化剂的开发，在双功能作用模式下，Ni (OH) 2 的边缘促进水的离解和氢中间体的产生， 然后吸附在附近的 Pt 位点上并重新结合成分子氢。[15]然而，一个关键问题仍然悬而未决；该方法能否成功应用于设计碱性溶液中的 HER 活性、经济高效的催化剂？到目前为止，传统的碱性水电解槽使用高表面积雷尼镍和镍合金[5e, 7]材料，这些材料更便宜但活性不够，从而为改善阴极反应动力学提供了广阔的空间。在这里，我们证明了经过Ni(OH)2纳米团簇修饰的Ni电极上的HER大约是裸露Ni表面的四倍，从而 提供了一种提高碱性电解槽经济有效的催化剂活性的方法。为了强调双功能机制的重要性，我们还报告了 IB 族（第 11 族）金属（M= Cu、Ag、Au）以及 Pt 族（第 10 族）金属（M= Ru、Ir、Pt）和 Ni (OH) 2 修饰的过渡金属（3d TMs= Ni、V、Ti）的 HER 结果。而不是尝试以火山式的方式呈现数据。 多方面（通常是深奥的）领域，这里的总体重点是提供对基本物理概念的直接分析以及对碱性 HER 元素周期表中活性趋势的实验见解。这些将通过与相应的酸性 HER 活性进行比较得到进一步支持。几十年来，酸性介质中 HER 金属催化剂的实际设计一直基于众所周知的火山图概念，[8] 它通常用于表达 HER 速率与金属的一些物理化学性质（描述符）之间的关系，例如氢吸附能，[9] 金属氢化物形成的大量热量，[10] 和金属功函数。 [11]除了极少数例外，[11b] 从实验结果 [11a] 和计算方法 [9b, c, 12] 中都发现了经典的火山形相关性，其中吸附氢既不强也不弱的金属（Pt 族金属）占据了火山曲线的顶点。虽然强烈吸附氢的金属（Ru 和 3d 元素）位于……的下降部分。
The hydrogen evolution reaction (HER) plays a key role in a number of technologically important areas such as water and chlor-alkali electrolysis,[1] metal deposition,[2] corrosion,[3] and fuel production from CO2 reduction.[4] The HER is also of fundamental importance, serving for decades as a model reaction for exploration of the relationship between the electrode material and the kinetic rates of electrochemical transformation of protons (acid) or water (alkaline) into molecular hydrogen (2 H+[2 H2O]+ 2eÀ QH2+[2 OHÀ]).[5] Traditionally, the mechanism of the HER is usually assumed to proceed by an initial formation of hydrogen intermediates (denoted hereafter as Had) which, depending on the pH value of solutions, is formed by an electron-transfer step through the discharge of protons or water (H+[H2O]+ eÀ QHad-[+ OHÀ]). This, so-called Volmer step, is then followed either by the Tafel chemical recombination step (2HadQH2) or by a second electron transfer through the Heyrovsky step (H+[H2O]+ Had+ eÀ QH2 [+ OHÀ]). Although the reaction pathways are similar because of the activated water dissociation step the HER activities for most catalysts in alkaline medium are usually about two to three orders of magnitude lower than in acid solutions.[5b, 6] This recognition initiated development of the Ni (OH) 2/Pt catalysts for which, in a bifunctional mode of action, the edges of Ni (OH) 2 promote the dissociation of water and the production of hydrogen intermediates that then adsorb on nearby Pt sites and recombine into molecular hydrogen.[15] However, one key question still remains open; can this method be successfully applied to design active, cost-effective catalysts for the HER in alkaline solutions. So far, the conventional alkaline water electrolyzers use high-surface-area Raney Ni and Ni alloys,[5e, 7] materials that are cheaper but not active enough, thus providing a significant scope for improving the reaction kinetics at the cathode.Here, we demonstrate that the HER on a Ni electrode modified by Ni (OH) 2 nanoclusters is about four times higher than on bare Ni surfaces, thereby providing a means to enhance the activity of cost-effective catalysts for alkaline electrolyzers. To emphasize the importance of the bifunctional mechanism, we also report the results for the HER on IB group (Group 11) metals (M= Cu, Ag, Au) as well for the Pt group (Group 10) metals (M= Ru, Ir, Pt) and transition metals (3d TMs= Ni, V, Ti) modified by Ni (OH) 2. Rather than attempting to present the data in a volcano-like fashion for this multifaceted (and often esoteric) area, the overall emphasis here is on providing a straightforward analysis of the underlying physical concepts and the experimental insights on the activity trends along the periodic table for the alkaline HER. These will be further supported by drawing comparisons with the corresponding acid HER activities. For decades, practical design of metal catalysts for the HER in acidic media has been based on the well-known concept of volcano plots,[8] which is generally used to express the relationship between the rate of the HER and some of the physicochemical properties (descriptors) of metals such as, for example, the hydrogen adsorption energies,[9] bulk heats of metal-hydride formation,[10] and the metal work function.[11] With rare exceptions,[11b] a classical volcano-shaped correlation is found from both experimental results [11a] as well as computational approaches [9b, c, 12] with metals that adsorb hydrogen neither strongly nor weakly (the Pt group metals) occupying the apex of the volcano curve. While the metals that adsorb hydrogen strongly (Ru and 3delements) are positioned on the descending part of …