Institute for Superconducting and Electronic Materials, Australian Institute for Innovative Materials, University of Wollongong, Wollongong, NSW 2522, Australia.
Nanoscale. 2019 Jan 3;11(2):717-724. doi: 10.1039/c8nr08028c.
The sluggish reaction kinetics of the hydrogen evolution reaction (HER) in alkaline media is a great obstacle to alkaline water electrolysis, and it remains a great challenge to develop precious metal-free efficient catalysts for the alkaline HER. Transition metal dichalcogenides (TMDs), in particular MoS2 and MoSe2, are promising catalysts for the HER in acidic media, but they exhibit much inferior catalytic activity for the alkaline HER owing to the slow water dissociation process. In this work, we, for the first time, demonstrate that TMD heterostructures with abundant edge sites deliver substantially accelerated alkaline HER kinetics, which is in great part due to the enhanced water adsorption/dissociation capability. As a proof of concept, MoS2/MoSe2 heterostructures with ultrasmall MoS2 nanoclusters anchored on MoSe2 nanosheets are synthesized via a solution-phase process and are investigated as alkaline HER catalysts in detail. MoSe2 nanosheets serve as excellent substrates to hinder the agglomeration of MoS2 nanoclusters, resulting in abundant edge sites. Benefiting from the decent water adsorption/dissociation capability of the edge sites, the optimal MoS2/MoSe2 heterostructure shows exceptional catalytic activity in 1 M KOH with an overpotential of 235 mV at 10 mA cm-2 and a Tafel slope of 96 mV dec-1, which is substantially improved as compared with the individual MoSe2 (330 mV, 135 mV dec-1) and MoS2 (400 mV, 157 mV dec-1). The success of this catalyst design strategy for enhancing alkaline HER kinetics is also demonstrated in MoSe2/MoSe2 and MoS2/MoS2 heterostructures. The results suggest that engineering additional edge sites that have a strong affinity for H2O is critical for TMDs towards enhanced alkaline HER activity, and also open new avenues in the design of precious metal-free efficient catalysts for the alkaline HER.
在碱性介质中，析氢反应（HER）的缓慢反应动力学是碱性水电解的一大障碍，开发用于碱性 HER 的无贵金属高效催化剂仍然是一个巨大的挑战。过渡金属二硫属化物（TMDs），特别是 MoS2 和 MoSe2，是酸性介质中 HER 的有前途的催化剂，但由于水离解过程缓慢，它们对碱性 HER 的催化活性要差得多。在这项工作中，我们首次证明具有丰富边缘位点的 TMD 异质结构可大大加速碱性 HER 动力学，这在很大程度上归因于增强的水吸附/离解能力。作为概念验证，通过溶液相过程合成了具有锚定在 MoSe2 纳米片上的超小 MoS2 纳米团簇的 MoS2/MoSe2 异质结构，并详细研究了其作为碱性 HER 催化剂的性能。MoSe2 纳米片作为优异的基质可阻止 MoS2 纳米团簇的团聚，从而产生丰富的边缘位点。得益于边缘位点良好的水吸附/离解能力，优化的 MoS2/MoSe2 异质结构在 1 M KOH 中表现出优异的催化活性，在 10 mA cm-2 时的过电位为 235 mV，塔菲尔斜率为 96 mV dec-1，与单独的 MoSe2（330 mV，135 mV dec-1）和 MoS2（400 mV，157 mV dec-1）相比有了显著提高。这种用于增强碱性 HER 动力学的催化剂设计策略的成功也在 MoSe2/MoSe2 和 MoS2/MoS2 异质结构中得到了证明。结果表明，对于 TMDs 来说，构建对 H2O 具有强亲和力的额外边缘位点对于增强碱性 HER 活性至关重要，并且为设计用于碱性 HER 的无贵金属高效催化剂开辟了新途径。
