Construction And Modification Of Three-dimensional Electrode For Effective Electrocatalytic Hydrogen Evolution

Development of electrocatalysts with both excellent activity and high stability for hydrogen evolution reaction(HER) is essential for renewable energy research. Currently, electrocatalysts are often prepared in the form of powders. They are dispersed in solvents, casted onto electrodes or substrates, and then dried to assemble into membrane electrode. This process usually results in a limited catalyst/electrolyte contact area and unavoidable powder agglomeration, which greatly compromise the electrocatalytic performance. In contrast, three-dimensional(3D) electrode, which can be directly utilized as catalyst electrodes with sufficient catalyst/electrode contact area, good mechanical properties, enhanced HER catalytic activity and robust stability, could be a promising solution to this problem. However, only a few literatures have been reported where 3D electrodes were used as electrocatalysts directly for hydrogen evolution reaction. Recent research demonstrate that there are two main ways to construct effective and high stability 3D electrode. One is loading electrocatalyst on the 3D substrates such as carbon cloth, carbon fiber paper, another is building van der Waals heterostructures by using atomic-scale Lego. In this thesis, three 3D electrodes were fabricated and used as the working electrode directly. The details are listed below:(1) Hydrogen evolution reaction electrodes composed of Pt nanoparticles and MoS2 nanosheets grown on carbon fibers were prepared by a two-step reaction. Detailed electrochemical characterizations demonstrate that the Pt nanoparticles/MoS2 nanosheets/carbon fibers electrode(2.03 wt% Pt) exhibited an excellent catalytic activity for HER in an acidic electrolyte with an overpotential of 5 mV(vs. RHE). And the corresponding Tafel slope is estimated to be 53.6 mV/dec. Stability tests through long-term potential cycles and extended electrolysis confirm the exceptional durability of the catalyst.(2) MoS2 nanosheets-coated CoS2 nanowire arrays supported on carbon cloth(MoS2/CoS2/CC) were prepared by a two-step procedure that entailed hydrothermal growth of Co(OH)2 nanowire arrays on carbon cloth, followed by reaction with(NH4)2MoS4 to grow an overlayer of MoS2 nanosheets, which were cobalt and oxygen co-doped. Electrochemical studies showed that the obtained 3D electrode exhibited excellent HER activity with an overpotential of 87 mV(vs. RHE) at 10 mA/cm2, a small Tafel slope of 73.4 mV/dec and prominent electrochemical durability.(3) Cobalt nanoparticles embedded into the interlamination of N-doped graphene(Co@NGF) were fabricated by a simple vacuum filtration combined with subsequently controlled calcination. This flexible three-dimensional(3D) nano-architecture film directly used as electrode shows a low overpotential of only 14 m V(vs. RHE) with a small Tafel slope of 93.9 mV/dec for HER in 0.5 mol/L H2SO4. Stability tests through long term potential cycles and extended electrolysis confirm the perfect durability of Co@NGF in acid media. The remarkable HER catalytic activity is derived from the electronic penetration effect of cobalt nanoparticles as core protected by N-doped graphene as shell.In this paper, three effective 3D electodes were prepared for electrocatalytic hydrogen evolution reaction to lay a foundation for wearable electronics, roll-up displays, and other devices. Meanwhile, electrode architecture and compositions were study to understand the mechanism.