Synthesis Of Four Kinds Of Composite Materials And The Electrochemical Properties For Hydrogen Evolution Reaction

Energy shortage has become a global problem, and design of new high-performance material to cope with energy crisis has practical significance. Hydrogen energy is a kind of clean renewable energy which is high in calorific value and rich in resources. Electrochemical reduction of water is considered to be a viable and mature way among many techniques for hydrogen production because of its numerous advantages, such as easy operating and pollution-free.High-performance cathodic electrode material should possess many characteristics, including low hydrogen overpotential, large specific surface area, good electrical conductivity, excellent electrocatalytic activity and good electrochemical stability. However, its application in industry on a large scale was restrained because of the high energy consumption caused by high overpotential of hydrogen evolution reaction（HER） and low electrocatalytic activity. Therefore, it is significant to fabricate electrode with low overpotential and excellent electrocatalytic activity on HER in terms of energy conservation or from the long-term solution to energy problem.In this paper, in-situ polymerization, hydrothermal process and chemical reduction techniques were used to prepare four kinds of composite materials. Through experimental characterization of structure, morphology and electrochemical performance on HER, four kinds of composite electrodes present excellent electrocatalytic activity and good stability. The main contents of this work were as follows:（1） MoS₂/PANI composite material was prepared by hydrothermal method and the effect of different PANI content on the properties of HER was explored. The short rod-like morphology of PANI not only prevented agglomeration of MoS₂ nanospheres, but also improved the electrode conductivity of composite material. Compared with pure MoS₂ electrode（5 mA cm-2）, MoS₂/PANI electrode showed higher current density at overpotential of –400 mV. Wherein MoS₂/PANI-5 electrode with 19 wt% PANI showed the best HER activity with a current density of 80 mA cm-2 at –400 mV. It was noteworthy that Tafel slope of optimized MoS₂/PANI-5 was only 49 mV dec-1, which was smaller than that of pure MoS₂ without PANI（93 mV dec-1）.Meanwhile, Rct value of MoS₂/PANI-5 was smallest among 9 electrodes.The main reason was that the electrode with optimized PANI content improved electrical conductivity and caused the additional exposure of active edge sites.（2） CoS₂/MWCNTs composite material was prepared by hydrothermal process simply and the mechanism of improved HER caused by MWCNTs was studied. MWCNTs with large specific surface area and excellent electroconductivity prompted CoS₂ exposing more active edge sites. Compared with pure CoS₂ electrode（29 mA cm-2）,CoS₂/MWCNTs electrode exhibited larger cathodic current density of73 mA cm-2 at –400 mV. With the merits of more exposed active site and excellent electroconductivity of composite electrode, the novel CoS₂/MWCNTs electrode possessed smaller Tafel slope of 83 mV dec-1,as well as Rct of 310 Ω.（3） WS2/AB composite material was prepared based on large specific surface area and excellent electro-conductivity of Acetylene black（AB）,rich edge defects sites of WS2. Based natural layered silicate mineral–4A-zeolite as pore-forming agent, we prepared porous WS2/AB composite materials for HER. Experimental results indicated that porous WS2/AB electrode exhibited a much higher HER activity than that of WS2/AB electrode and WS2 electrode. The exchange current density of porous WS2/AB electrode is 1.6 times larger than that of WS2/AB electrode, 2.5 times of WS2 electrode at –400 mV. Meanwhile,the porous WS2/AB electrode possessed smaller Tafel slope, further proving the enhancement effect of HER activity by excellent electroconductivity of AB and porosity of 4A-zeolite.（4） PPy nanowires, which was in the preparation of aniline（ANI） by in-situ polyrization, was used as nucleation to chemical reduction Ni2+to Ni nanoparticles. We prepared Ni/PPy composite and studied the electrocatalytic activities of Ni/PPy/GCE towards HER. The exchange current density of Ni/PPy/GCE（93 mA cm-2） is 2.6 times larger than that of pure Ni/GCE（36 mA cm-2） at –400 mV. With the merits of PPy nanowires, the novel Ni/PPy/GCE exhibited low Tafel slope as well as Rct and excellent stability, revealing the significant enhancement of electrocatalytic performance.Four kinds of composite: MoS₂/PANI, CoS₂/MWCNTs, porous WS2/AB and nano Ni/PPy composite material were prepared in the study. They have the characteristics of high HER activity than the bulk counterpart,small Tafel slope and the excellent stability, which have promising prospect in electrochemical reduction of water.