Preparation And Properties Studies On The Hydrogen Electrode For Water Electrolysis

Hydrogen energy is a kind of clean renewable energy which has many prominent merits such as rich in resources and easy to store up. Because of the exhaustion of the fossil fuels and the environmental crisis, people have paid more attention to it. The main method to prepare hydrogen on a large scale is water electrolysis. In order to decrease cathode overpotential for reducing energy consumption, it’s of momentous significance to research new cathode electrode materials which have lower hydrogen-evolution overpotential and high catalytic activity. There are two important factors that can affect the catalytic activity of the hydrogen-evolution materials:energy factors and geometry factors. So there are two main methods can be taken to prepare cathode materials for hydrogen evolution which own high catalytic activity. One is to search for a new kind of catalytic materials of high catalytic activity so as to improve electrocatalytic activity of the electrode itself. The other is to increase the actual specific surface area of the electrode, namely to amplify the electrode surface roughness which can decrease the true current density of the electrode surface in the course of electrolysis reaction so as to reduce the cathode overpotential. This thesis mainly researched the preparation of the hydrogen-evolution electrode material of high catalytic activity by electrodeposition and characterized every electrode by SEM, EDS and XRD, and also analysised the electrochemical properties of hydrogen evolution reaction in 25 wt% KOH solution.Ni-Mo-Co alloy electrode was prepared by electrodeposition. Systematic researched the influence of the density of CoSO4·7H2O and Na2MoO4·2H2O, the electrodeposition current density, the electrodeposition temperature and the time on the catalytic activity of the alloy electrode, then fixed the optimal technics parameters of the preparation of the electrode. The SEM pictures of the prepared Ni-Mo-Co alloy electrode showed that the rough electrode surface consists of many cauliflower-like nanosize particles. EDS results proved that the atomic composition of the alloy was Ni41.33Mo49.13Co9.54; The XRD diffraction pattern proved that the alloy electrode was amorphous to a certain degree. By analysising the steady-state polarization cyclic voltammetry, it could be found that the Ni-Mo-Co alloy electrode showed high apparent exchang current density for the hydrogen evolution reaction. Under the same conditions, Ni-Mo-Co alloy electrode overpotentialη100(i=100 mA/cm2) is 0.188 V, which was about 0.295 V lower than Ni electrode. Its catalytic activity is also higher than the electrode of Ni-Mo alloy, Ni-Co alloy and Ni. As the three elements of Ni, Mo, Co formed ternary amorphous which own lower apparent activation energy of hydrogen-evolution reaction and high surface roughness. The combined action of the energy factors and geometry factors brought about exceptional catalytic activity for the Ni-Mo-Co alloy electrode.The optimal technics conditions for preparing Ni-Mo-Fe alloy electrode were fixed by orthogonal and single factor experimentation. From the SEM pictures, it could be found that a large number of spherical particles are distributed on the alloy surface which is prepared under the optimal technics conditions. These particles could increase the electrode surface roughness and be beneficial to the hydrogen-evolution reaction; EDS results proved that the composition of atoms of the alloy is Ni24.77Mo42.21Fe33.02; The test of XRD showed that the Ni-Mo-Fe alloy electrode ranged between crystalline and amorphous. The electrochemical properties showed that the Ni-Mo-Fe alloy electrode had a larger exchange current density and lower overpotential, higer activity for hydrogen evolution. By comparing with the Ni-Mo-Co alloy electrode, it could be found that the Ni-Mo-Fe alloy electrodes own higher apparent activation, lower surface roughness, larger resistance and lower hydrogen-evolution catalytic activity.After the comprehensive analysis of the energy factors and the geometry factors, the Ni-Mo-Co alloy electrode of high hydrogen-evolution catalytic activity was chosen. The polyurethane was used as the electrode substrate. After pretreatment, electroless nikel, electrodeposition of Ni-Mo-Co alloy and thermal decomposition, the Ni-Mo-Co alloys foams electrode was obtained. The influence of the deposition current density on the electrode catalytic activity was researched. The results proved that the alloy electrodes prepared by the deposition current density of 8A/dm2 possess the highest catalytic activity. From the SEM pictures of the Ni-Mo-Co alloy foams electrode, it could be found that the alloy electrode had three-dimensional structure of the framework, a large number of micro-cracks of the skeleton and uniforn dense spherical particles of the surface, its surface microstructure was rough. The test of XRD showed that the alloy electrode was crystalline state which was of higher stability when compared with amorphous. The electrochemical experiment showed that the overptentialη100(100mA/cm2) andη200(i=200mA/cm2) of the Ni-Mo-Co alloy foams electrode were 65 mV and 63 mV lower than the Ni-Mo-Co alloy electrode respectively. The main reason for that was the geometry factors. This electrode has quite large specific surface area and its surface roughness r is 80.5 times and 197.6 times as much as Ni-Mo-Co alloy and Ni-Mo-Fe alloy respectively. The square wave potential cures showed that the surface of the Ni-Mo-Co alloy foams is 5.8 times as much as the Ni foams.