Preparation Of Cobalt,Nickel And Iron-Based Self-Supported Electrodes And Their Catalytic Performance Of Water-Ethanol Electrolysis For Hydrogen Production

Owing to the sluggish kinetics of anodic oxygen evolution reaction(OER),the electrical efficiency of hydrogen production via water electrolysis is discontented.This is the bottleneck problem that restricts its application.By adding more favourable electro-oxidized organics to the aqueous electrolyte and replacing the OER with the organic electrooxidation reaction on the anode,the overpotential can be decreased,thereby improving the electrical efficiency of the hydrogen production.Meanwhile,it can produce more valuable organic products and simplify the structure of electrolytic cell.This strategy has become one of the hot spots in recent years.In this work,the preparation of self-supported electrodes based on the sulfide,selenide and phosphide catalysts of cheap transition metals cobalt,nickel and iron is studied for the electrolysis of hydrogen production in water-ethanol binary system.The effect of the composition and structure of the catalytic electrode on the electrocatalytic performance of ethanol oxidation reaction(EOR)and water reduction hydrogen evolution(HER)reaction in water-ethanol binary electrolyte system is investigated.The symmetrical two-electrode electrolysis devices are assembled with the as-prepared electrodes as cathode and anode,and their performance in hydrogen production by electrolysis in water-ethanol binary electrolyte system and pure water system are investigated.Phosphorus-doped cobalt sulfide nanosheet array electrode supported on carbon cloth(Co-S-P/CC)is prepared by hydrothermal and low-temperature phosphating reactions.The XRD and XPS results show that the structure of Co-S-P is similar to that of cubic pyrite type Co S₂.SEM and TEM show that Co-S-P are the two-dimensional nanosheets structure composed of many nanoparticles,which are cross-linked with each other.The electrochemical test results show that the potential of ethanol oxidation of Co-S-P/CC electrode is only 1.38 V at the current density of 10 m A·cm^-2 in 1.0 mol·L^-1 ethanol and 1.0 mol·L^-1 KOH electrolyte,which is lower than that of precious metal Pt-C/CC(1.46 V).Moreover,the electrocatalytic stability can be maintained for 20 h.Nuclear magnetic resonance(NMR)results show that ethanol is oxidized to acetic acid at Co-S-P/CC electrode,which exists in the form of CH₃COO^-in the alkaline medium.The potential of Co-S-P/CC electrode is-0.167 V at 10m A·cm^-2 toward HER.The electrolytic voltage of Co-S-P/CC//Co-S-P/CC water-ethanol electrolytic cell is 1.63 V at the current density of 10 m A·cm^-2,which is 140 m V less than that of single water electrolysis.It shows that the electrolysis efficiency of hydrogen production by water ethanol system with Co-S-P/CC as the symmetrical electrode is higher than that traditional alkaline water electrolysis.Sulphur spinel-type of CuCo₂S₄ array supported on carbon cloth(CuCo₂S₄/CC)is obtained by a two-step hydrothermal method.SEM and TEM show that hollow needle-like structure CuCo₂S₄ are uniformly grown on the carbon cloth.The average thickness of the needle wall is about 22 nm.The electrocatalytic test results show that the CuCo₂S₄/CC electrode exhibits the optimum EOR and HER activity.At a current density of 10 m A·cm^-2,the potential of CuCo₂S₄/CC is-0.166 V for HER and 1.38 V for EOR,outperforming most of Cu,Co-based non-noble metal catalysts toward alcohol electrooxidation.The CuCo₂S₄/CC//CuCo₂S₄/CC water-ethanol electrolytic cell only requires the voltage 1.59 V to reach a current density of 10 m A·cm^-2,which is 150 m V lower than that of sole water electrolysis.After 30 h continuous operation,the electrolytic voltage is still maintained.NMR test results show that the liquid product of the water-ethanol system electrolysis with CuCo₂S₄/CC as the symmetric electrode is mainly acetic acid,which exists in the form of CH₃COO^–in the alkaline medium.A series of Co doped Ni_0.85Se materials are fabricated on carbon cloth by a two-step hydrothermal method.XRD test results show that with the increase of Co doping amount,the crystallinity of the material gradually becomes weakened and the disorder increases.SEM shows that after Co doping,Ni0.85Se changed from two-dimensional nanosheets that are cross-linked to one-dimensional nanowires with edge-grown nanosheets.With the increase of the relative content of Co,the length and diameter of the nanowires increase.The electrocatalytic activity of samples under different ratios of Ni and Co is investigated by electrochemical methods.It is found that when the ratio of Ni to Co is 9:1,the formed of(Ni_0.9Co_0.1)_0.85Se/CC has the best EOR and HER activity.At current densities of 10 and 100m A·cm^-2,the ethanol oxidation potential of the(Ni_0.9Co_0.1)_0.85Se/CC electrode is only 1.34 V and 1.41 V,outperforming most of the reported Ni,Co-based catalysts for ethanol electrooxidation.The potential of(Ni_0.9Co_0.1)_0.85Se/CC electrode is-0.168 V to provide a current density of 10 m A·cm^-2 for HER.At a current density of 10 m A·cm^-2,the electrolysis voltage of the(Ni_0.9Co_0.1)_0.85Se/CC//(Ni_0.9Co_0.1)_0.85Se/CC water-ethanol electrolytic cell is1.57 V,which is 110 m V lower than that of pure water electrolysis.It shows that the water-ethanol system with(Ni_0.9Co_0.1)_0.85Se/CC as the symmetric electrode has lower energy consumption than water electrolysis alone.The nickel-iron phosphide nanosheet array electrode supported on foamed nickel(Ni-Fe-P/NF)is prepared by the hydrothermal method and low-temperature phosphating method.SEM and TEM show that 2D Ni-Fe-P nanosheets rich in nanopores are grown on the conductive foam nickel framework,and the thickness of the nanosheets is between 30-50 nm.The unique structure of Ni-Fe-P has a large specific surface area(106.8 m²g^?1).The formation of nanopores increases the number of exposed active sites,which not only facilitates the electrolyte penetration and mass transfer process,but also contributes to the rapid dissipation of gaseous products,thereby improving its catalytic performance.The EOR and HER performance of Ni-Fe-P/NF is measured in three-electrode system.At a current density of 10m A·cm^-2,the potential of Ni-Fe-P/NF is-0.156 V for HER and only 1.36 V for EOR.The symmetrical ethanol-water electrolysis cell assembled with Ni-Fe-P/NF as the cathode and anode only needs 1.53 V voltage to reach a current density of 10 m A·cm^-2,which is 130 m V lower than the sole water electrolysis.After 30 hours of continuous operation,the electrolysis voltage is still maintained.These performances outperform most of the reported hydrogen production devices by electrolysis of water.