(Digital Presentation) Hydrothermal Electrodeposition of Molybdenum Sulfide Toward Electrochemical CO2 Reduction Catalysts

Abstract

The search and development of efficient carbon dioxide (CO2) reduction reaction electrocatalysts is a hot topic in this era of global warming. Among material candidates for sustainable and cost−effective applications, metal sulfides have attracted attention as promising nature-inspired materials due to multiple adsorption sites which are enhanced by the covalent character of sulfur.Molybdenum sulfides (MoS2) is one of the trandition metal dichalcogenides (TMDs) and possesses three kinds of struture; namely, metastable octahedral structure with high electronic conductivity (1T), stable triangular prism structure with low electronic conductivity (2H) and insulating rhombohedral structure (3R). Among them, 1T phase has been widely applied as catalysts for various reactions such as electrochemical nitrogen reduction reaction and electro/photochemical hydrogen evolution reaction. Since the structure of MoS2 largely affect its catalytic and other material property, synthetic process to control their bulk and even local structure should be explored to expand their availability as functional materials. Especially, our previous work (J. Phys. Chem.C, 126, 2772, 2022) demonstrated that metal-sufur bonding length is one of the key parameter to control carbon monoxide production selectivity from electrochemical CO2 reduction.Here in this work, hydrothermal electrodeposition was applied to MoS2 synthesis to control their local structure. Recently, our group developed hydrothermal electrochemical flow reactor which enables the electrochemistry under hydrothermal condition with separate control of temperature and pressure. Using this reactor, hydrothermal electrodeposition of manganese oxides (MnO2) was conducted and samples exhibited higher electrochemical oxygen evolution activity than ones prepared with conventional methods. Also, the characterization results of electrodeposited MnO2 under hydrothermal condition showed the possiblity that morphology and lattice spacing can be controled by changing deposition temperature and pressure, respectively. Thus, we predicted our hydrothermal electrodeposition technique is useful to control the local structure of materials.The hydrothermal electrodeposition of MoS2 were conducted under various temperature and pressure conditions and those samples were characterized with X-ray diffraction (XRD). Also, the effect of the deposition temperature and pressure on sample local structure was examined with Pair Disribution Function analysis of XRD and Extended X-ray Absorption Fine Structure analysis using synchrotron radiation. The electrochemical CO2 reduction experiments using hydrothermally depositted MoS2 samples revealed that the product selectivity for CO2 reduction was changed with deposition pressure. Thus, we confirmed that our hydrothermal electrochemical deposition can be applicable to the synthesis of metal sulfide-based CO2 reduction electrocatalysts, whose local structures are tuned.