School of Engineering, Engineering Research Institute, Ulster University, Newtownabbey BT37 0QB, UK.
Nanoscale. 2017 Sep 21;9(36):13515-13526. doi: 10.1039/c7nr04790h.
The rational design of transition metal dichalcogenide electrocatalysts for efficiently catalyzing the hydrogen evolution reaction (HER) is believed to lead to the generation of a renewable energy carrier. To this end, our work has made three main contributions. At first, we have demonstrated that exfoliation via ionic liquid assisted grinding combined with gradient centrifugation is an efficient method to exfoliate bulk WS to nanosheets with a thickness of a few atomic layers and lateral size dimensions in the range of 100 nm to 2 nm. These WS nanosheets decorated with scattered nanodots exhibited highly enhanced catalytic performance for HER with an onset potential of -130 mV vs. RHE, an overpotential of 337 mV at 10 mA cm and a Tafel slope of 80 mV dec in 0.5 M HSO. Secondly, we found a strong aging effect on the electrocatalytic performance of WS stored in high boiling point organic solvents such as dimethylformamide (DMF). Importantly, the HER ability could be recovered by removing the organic (DMF) residues, which obstructed the electron transport, with acetone. Thirdly, we established that the HER performance of WS nanosheets/nanodots could be significantly enhanced by activating the electrode surface at a positive voltage for a very short time (60 s), decreasing the kinetic overpotential by more than 80 mV at 10 mA cm. The performance enhancement was found to arise primarily from the ability of a formed proton-intercalated amorphous tungsten trioxide (a-WO) to provide additional active sites and favourably modify the immediate chemical environment of the WS catalyst, rendering it more favorable for local proton delivery and/or transport to the active edge site of WS. Our results provide new insights into the effects of organic solvents and electrochemical activation on the catalytic performance of two-dimensional WS for HER.
用于高效催化析氢反应 (HER) 的过渡金属二卤化物电催化剂的合理设计被认为是产生可再生能源载体的关键。为此，我们的工作做出了三个主要贡献。首先，我们证明了离子液体辅助研磨与梯度离心相结合的剥离方法是将块状 WS 剥离成具有几个原子层厚度和 100nm 至 2nm 范围内的横向尺寸的纳米片的有效方法。这些带有分散纳米点的 WS 纳米片表现出对 HER 具有高度增强的催化性能，其起始电位为 -130mV 相对于 RHE，在 0.5M HSO 中 10mA cm 时的过电位为 337mV，塔菲尔斜率为 80mV dec。其次，我们发现 WS 在高沸点有机溶剂（如二甲基甲酰胺 (DMF)）中储存时存在强烈的老化效应。重要的是，通过用丙酮去除阻碍电子传输的有机（DMF）残留物，可以恢复 WS 的 HER 能力。第三，我们发现通过在短时间内（60s）将电极表面在正电压下激活，可以显著增强 WS 纳米片/纳米点的 HER 性能，在 10mA cm 时降低超过 80mV 的动力学过电位。发现性能增强主要归因于形成的质子插层无定形三氧化钨 (a-WO) 的能力，它提供了额外的活性位点，并有利地改变了 WS 催化剂的直接化学环境，使其更有利于局部质子传递和/或传输到 WS 的活性边缘位点。我们的结果为有机溶剂和电化学激活对二维 WS 用于 HER 的催化性能的影响提供了新的见解。
