Study On Preparation And Hydrogen Evolution Performance Of Cathode Materials For Microbial Electrolysis Cells

With the continuous development of economy,energy shortage and environmental pollution problems have become more and more serious,and vigorous development of renewable clean energy has become one of the most urgent tasks and topics.Microbial electrolytic cells?MECs?use microorganisms to degrade pollutants in organic wastewater and simultaneously generate hydrogen at the cathode,which can protect the environment and alleviate energy shortages to a certain extent.Cathode is the core technology of MEC catalytic hydrogen production.It is of great significance to develop a new high-efficiency cathode catalyst that can replace Pt to reduce cost.In this paper,MECs cathode hydrogen evolution catalysts were prepared by two different methods:single Ni,Co and composite Ni/Co were deposited on carbon paper by constant potential method;single Ni and composite Mo/Ni were deposited on carbon paper by cyclic voltammetry.The electrochemical properties of the cathode materials were investigated by linear sweep voltammetry,AC impedance,Tafel polarization,chronoamperometry and chronopotentiometry.The surface morphology,crystal form,elemental composition and valence state of the material were investigated by SEM,XRD and XPS.The specific research contents are as follows:?1?Preparation of Ni,Co and Ni/Co cathode materials by electrodeposition with potentiostatic method and the research of their hydrogen evolution propertiesThe carbon-based Ni,Co and Ni/Co were separately prepared by the potentiostatic method and used as the MEC cathode material.The SEM image shows that the carbon-based Ni is spherical particles that uniformly covered on the carbon paper;Co is stacked by the vertical lamellar structure to form a spherical shape;Ni/Co is composed of tight needle-shaped pieces.In the MEC hydrogen production experiment,the current densities of the carbon-based Ni,Co and Ni/Co cathodes were 15.31,10.93 and 12.26 A m^-2 at an applied voltage of0.7 V,and the gas volumes generated was 11.40,8.5 and 10.09 mL,respectively.Linear sweep voltammetry and cyclic voltammetry tests show that the hydrogen evolution performance of Ni cathode is significantly better than that of Co and Ni/Co cathodes.The Tafel curve tests show that the Tafel slope of the Ni cathode?59.89 mV dec-1?is the lowest compared to the two mentioned before.?2?Preparation of Ni and Mo/Ni cathode materials by cyclic voltammetry electrodeposition and the research of their hydrogen evolution propertiesCarbon-based Ni and Mo/Ni were separately prepared by cyclic voltammetry and used as the MEC cathode material.At an applied voltage of 0.7 V,the current density and hydrogen volume generated by Mo/Ni are higher than Ni,even higher than Pt.Linear sweep voltammetry,chronoamperometry,chronoamperometry and Tafel curve tests show that the electrochemical performance of Mo/Ni is better than Ni.SEM shows that the Mo/Ni material exhibits a two-dimensional sheet structure,and the XRD pattern indicates that the Mo/Ni material structure is amorphous.The XPS tests show that the valence state of Mo in the material is+4and+6,and the valence of Ni is+2.Therefore,the cyclic voltammetry deposition products are consisted of NiO/MoO₂/MoO₃.During the one-month operation of the experiment,the current density and hydrogen production capacity of NiO/MoO₂/MoO₃ cathode were stable,indicating that the catalytic stability of the cathode was good.