MoS2/GQDs催化剂的制备及微生物电解池的产氢性能研究

通过水热法合成了一系列MoS₂/GQDs复合材料,并制成碳基复合电极。利用电化学测试手段挑选出最佳电极后用于微生物电解池（MEC）阴极的产氢性能研究。实验结果显示： Na₂MoO₄、半胱氨酸和GQDs的最佳原料配比为375:600:1,制备出的MoS₂/GQDs呈现明显的爆米花样纳米片结构,片层厚度在10 nm左右,当碳纸负载量为1.5 mg·cm^-2时,MoS₂/GQDs碳纸电极的析氢催化能力最佳。在MEC产氢实验中,MoS₂/GQDs阴极MEC的产气量、氢气产率、库仑效率、整体氢气回收率、阴极氢气回收率、电能回收率和整体能量回收率分别为51.15±3.15 mL·cycle^-1、0.401±0.032 m³H₂·m³d^-1、91.16±0.054%、66.64±5.39%、72.44±2.60%、217.26±7.42%和77.37±1.50%,均略高于Pt/C阴极MEC或与之媲美。另外,MoS₂/GQDs具有良好的长期稳定性,且价格便宜,有利于实际应用。

Preparation and Electrochemical Evaluation of MoS2/Graphene Quantum Dots as a Catalyst for Hydrogen Evolution in Microbial Electrolysis Cell

Microbial electrolysis cell (MEC) is a relatively new bioelectrochemical technology that produces H₂ and meanwhile treats organic wastewater. Cathode hydrogen evolution catalyst plays a key role in MEC. The doping of Graphene Quantum Dots (GQDs) into MoS₂ nanosheets can improve the catalytic activity of MoS₂ by creating abundant defect sites both in the edge plane and the basal plane, as well as enhancing the electrical conductivity. In this paper, using Na₂MoO₄ , cysteine and GQDs as raw materials, a series of MoS₂/GQDs composites were firstly synthesized via hydrothermal method, and then loaded on the carbon-based electrode. The optimal electrode was selected by electrochemical testing methods and used as a cathode of MEC to research the hydrogen production capacity. SEM image showed that the MoS₂/GQDs composite exhibited a popcorn-like nanosheet structure and the thickness of each nanosheet was about 10 nm. The specific surface area of MoS₂/GQDS composite reached 67.155 m²·g^-1, which was 16 times of the specific surface area of MoS₂ (4.197 m²·g^-1). TEM image showed that some lattice fringes representing GQDs were intermixed with lattice fringes representing MoS₂, which indicated that GQDs were well embedded in MoS₂ . EDS results showed that the MoS₂/GQDS composite contained Mo, S, C and O, and the atomic ratio of Mo: S: C: O = 1:2.5:1.9:1.2, indicating that the majority of Mo and S in the composite existed in the form of MoS₂, while a part of S existed in the form of SO_x. The LSV data of MoS₂/GQDs carbon paper electrode showed that the synthesized MoS₂/GQDs composite (2#) had the best catalytic activity toward hydrogen evolution when the raw material ratio of Na₂MoO₄, cysteine and GQDs was 375:600:1 with the optimum load of 1.5 mg·cm^-2. The Tafel slope of MoS₂/GQDs electrode (2#, 1.5 mg·cm^-2) was found to be 44.3 mV·dec^-1, lower than that of pure MoS₂ electrode, which indicated that the doping of GQDs into MoS₂ nanosheets made the electron transport more efficiently and the interfacial resistance was significantly reduced. In the MEC tests, the maximum hydrogen current density of MoS₂/GQDS cathode (2#, 1.5 mg·cm^-2) MEC reached 14.70 ± 0.80 A·m^-2, which was comparable to that of Pt/C cathode MEC (14.58 ± 0.92 A·m^-2), indicating that MoS₂/GQDS had a good catalytic activity for hydrogen evolution. The gas production, hydrogen production rate, coulombic efficiency, hydrogen recovery efficiency, cathodic hydrogen recovery efficiency, electrical and overall energy recovery efficiencies of MoS₂/GQDs cathode (2#, 1.5 mg·cm^-2) MEC were, respectively, 51.15±3.15 mL·cycle^-1, 0.40±0.032 m³H₂·m^-3d^-1, 91.16±0.054%, 66.64±5.39%, 72.44±2.60%, 217.26±7.42% and 77.37±1.50%, which were slightly higher than or comparable to those of Pt/C cathode MEC. In addition, MoS₂/GQDs enjoyed good stability and price advantage, which might promote the practical application of MECs.