Preparation Of Cobalt-based Hydrogen Evolution Catalysts And Their Application To Hydrogen Production Performance In MEC

With the rapid development of the global economy,the world is facing two major problems:1.the increasing depletion of traditional energy sources;2.the increasingly serious problem of environmental pollution.The search for green and sustainable alternative energy sources and the solution of environmental pollution problems has become a hot research topic for researchers.As the most promising green and pollution-free clean energy in the 21st century,the clean hydrogen production system includes:electrolysis of water to produce hydrogen,photolysis of water to produce hydrogen,photoelectric combination of decomposing water to produce hydrogen,microbial electrolysis cell（MEC）to produce hydrogen and so on.Among them,photolytic water hydrogen production and photoelectric combined decomposition water hydrogen production technologies are not yet mature;although electrolytic water hydrogen production system is relatively mature at present,it is limited by high power consumption and high cost;however,microbial electrolytic cell（MEC）hydrogen production can realize both wastewater treatment and electric energy or hydrogen energy recovery under the condition of low energy consumption,which can,to a certain extent,solve the problem of wastewater resources at the same time.To a certain extent,it can simultaneously solve the problems of efficient utilization of wastewater resources and mitigation of energy depletion.The cathode is the key to catalytic hydrogen evolution in the microbial electrolytic cell（MEC）hydrogen production system,and the development of inexpensive,efficient and stable catalysts for hydrogen evolution has become a problem that must be solved to realize the full-scale hydrogen production in microbial electrolytic cellsIn this thesis,a series of inexpensive,efficient and stable non-precious metal Co-based hydrogen precipitation catalysts were developed and used for the first time in a microbial electrolytic cell（MEC）system for the preparation of hydrogen.The performance of the hydrogen evolution catalysts was improved by modulating the microstructure of the catalysts to expose more active sites.In addition,we investigated the structure,morphology and electrochemical properties of the composite hydrogen evolution catalysts to explore the mechanism of hydrogen evolution in microbial electrolytic cell（MEC）.Details are as follows:（1）Using hydrothermal method to grow 3D cactus-shaped Co（OH）F in situ on foamed nickel to obtain a Co（OH）F/NF composite hydrogen evolution catalyst,which was used as the cathode hydrogen evolution material in MEC for the first time.The Co（OH）F/NF composite electrode can effectively increase the specific surface area,expose more active sites,enhance the electron transport ability,and provide a channel for the release of gas.The final test hydrogen production reached 0.89±0.04(m³·m^-3·d^-1).The Tafel slope of the composite electrode reaches 61.84(m V·dec^-1),and the linear scanning results show that the catalytic performance of the Co（OH）F/NF composite electrode is better than that of the blank nickel foam electrode.（2）Using the hydrothermal method to deposit durian-like CoFe₂O₄lamellae on the pre-treated foamed nickel（NF）substrate to obtain a CoFe₂O₄/NF composite hydrogen evolution catalyst.Then,the fluffy Co Ni-LDH was deposited on CoFe₂O₄/NF by unipolar pulse electrochemical deposition technology to obtain a Co Ni/CoFe₂O₄/NF composite hydrogen evolution catalyst.For the first time,it was applied to hydrogen production in the MEC system of microbial electrolytic cells.Under the condition of an applied voltage of 0.7V,the Co Ni/CoFe₂O₄/NF composite hydrogen evolution catalyst was compared with Co Ni/NF and CoFe₂O₄/NF,and the current densities were 30.45(A·m^-2),27.25(A·m^-2),23.77(A·m^-2),respectively.The amount of hydrogen produced is 1.25±0.06(m³·m^-3·d^-1),0.63±0.03(m³·m^-3·d^-1),0.52±0.02(m³·m^-3·d^-1).Scanning linear voltammetry and Tafel slope analysis both show that the hydrogen evolution performance of the Co Ni/CoFe₂O₄/NF composite catalytic material is better than that of the Co Ni/NF and CoFe₂O₄/NF composite electrodes.