Kundu Avinava, Chakraborty Biswarup
Department of Chemistry, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016, India.
JACS Au. 2024 Jan 17;4(2):642-656. doi: 10.1021/jacsau.3c00703. eCollection 2024 Feb 26.
The semiconducting behavior of mixed-valence copper sulfides arises from the pronounced covalency of Cu-S bonds and the exchange coupling between Cu and Cu centers. Although electrocatalytic study with digenite CuS and covellite CuS has been performed earlier, detailed redox chemistry and its interpretation through lattice structure analysis have never been realized. Herein, nanostructured CuS and CuS are prepared and used as electrode materials to study their electrochemistry. Powder X-ray diffraction (PXRD) and microscopic studies have found the exposed surface of CuS to be d(0015) and d(002) for CuS. Tetrahedral () Cu, distorted octahedral (O) Cu, and trigonal planar (T) Cu sites form the d(0015) surface of CuS, while the (002) surface of CuS consists of only Cu. The distribution of Cu and Cu sites in the lattice, predicted by PXRD, can further be validated through core-level Cu 2p X-ray photoelectron spectroscopy (XPS). The difference in the electrochemical response of CuS and CuS arises predominantly from the different copper sites present in the exposed surfaces and their redox states. In situ Raman spectra recorded during cyclic voltammetric study indicates that CuS is more electrochemically labile compared to CuS and transforms rapidly to CuO/CuO. Contact-angle and BET analyses imply that a high-surface-energy and macroporous CuS surface favors the electrolyte diffusion, which leads to a pronounced redox response. Post-chronoamperometric (CA) characterizations identify the potential-dependent structural transformation of CuS and CuS to CuO/CuO/Cu(OH) electroactive species. The performance of the in situ formed copper-oxides towards electrocatalytic water-splitting is superior compared to the pristine copper sulfides. In this study, the redox chemistry of the CuS/CuS has been correlated to the atomic arrangements and coordination geometry of the surface exposed sites. The structure-activity correlation provides in-depth knowledge of how to interpret the electrochemistry of metal sulfides and their in situ potential-driven surface/bulk transformation pathway to evolve the active phase.
混合价态硫化铜的半导体行为源于Cu-S键显著的共价性以及Cu中心之间的交换耦合。尽管之前已对辉铜矿CuS和铜蓝CuS进行了电催化研究，但详细的氧化还原化学及其通过晶格结构分析的解释从未实现。在此，制备了纳米结构的CuS和CuS并用作电极材料来研究它们的电化学性质。粉末X射线衍射（PXRD）和显微镜研究发现，CuS的暴露表面为d(0015)，CuS的暴露表面为d(002)。四面体（）Cu、扭曲八面体（O）Cu和三角平面（T）Cu位点构成了CuS的d(0015)表面，而CuS的（002）表面仅由Cu组成。PXRD预测的晶格中Cu和Cu位点的分布可通过芯能级Cu 2p X射线光电子能谱（XPS）进一步验证。CuS和CuS电化学响应的差异主要源于暴露表面存在的不同铜位点及其氧化还原状态。循环伏安研究期间记录的原位拉曼光谱表明，与CuS相比，CuS在电化学上更不稳定，并且会迅速转变为CuO/CuO。接触角和BET分析表明，高表面能和大孔的CuS表面有利于电解质扩散，这导致明显的氧化还原响应。计时电流（CA）后表征确定了CuS和CuS向CuO/CuO/Cu(OH)电活性物种的电位依赖性结构转变。原位形成的氧化铜对电催化水分解的性能优于原始硫化铜。在本研究中,CuS/CuS的氧化还原化学与暴露表面的原子排列和配位几何结构相关。结构-活性相关性提供了关于如何解释金属硫化物的电化学及其原位电位驱动的表面/体相转变途径以形成活性相的深入知识。
