Preparation Of The Nickel-cobalt Compound Oxides Active Anodes And Studies Their Performances In The Oxygen Evolution Reaction

In the industry of water electrolysis for Hydrogen production, the higher anodic overpotential for oxygen evolution reaction is the main reason for the lower energy transformation in the course of electrolysis. So it is an important task to research and prepare the high activity anodic electrode materials to decrease the overpotential of oxygen evolution reaction in alkaline water electrolysis at the present time. There are many kinds of anodic materials that own good electrocatalytic activity for the oxygen evolution reaction. But only a few can be applied in the industrial production. When the practicality is taken into account, the electrode materials of industrial using should possess everal characters: (1) Higher specific surface areas. (2) Higher electric conduction. (3) Higher electrocatalytic activity. (4) Longer stability of mechanism and chemistry. (5) Little air bladder separating out. (6) Higher selectivity. (7) Easy preparation and low cost. (8) Security. Because of higher practical current density, (2), (3), (4) three points are very important. Because of higher electric conduction may decrease energy loss, which are caused by ohm polarization. Longer stability may bring longer life of electrode materials. Higher catalytic activity is the primary way of many ones to decrease the anodic overpotential in the oxygen evolution reaction. That is also one import index of estimating the performance of the electrodes. So it should be regarded especially. This paper mainly researched the preparation and application of high catalytic activity electrode materials for evolution oxygen reaction. The mainly research content of this paper is as follows:1. The nickel foam was used as the electrode substrate, and immerged into the mixed solution containing Ni(NO3)2, Co(NO3)2 and Ce(NO3)3 for cathodal electrodeposit to obtain Ni(OH)2, Co(OH)2 and Ce(OH)3 complex film. Then it was thermally decomposed at 300℃. After the conversion, the nickel foam/Ni-Ce-Co-O compound oxides film electrode was obtained. Then its catalytic performance was tested with electrochemical mothod. By contrast with the nickel foam electrode and the nickel foam/Ni-Co-O electrode, it was obvious that the nickel foam/Ni-Ce-Co-O electrode owns better electrocatalytic activity. In 30% KOH solution, at 4000A/m2 current dentity, its polarization potential was 0.641V, which was 129mV lower than the nickel foam electrode and 46mV lower than the nickel foam/Ni-Co-O electrode. Thus, the thulium Ce was adulterated into the Ni-Co-O oxides could improve the electrocatalytic activity of the electrode obviously. The best experimental condition of preparing the electrode was as follows: the thermal decomposing temperature was 300℃, the current density for cathodal deposition was 8mA/cm2, the time of deposition was 30min, when 40ml 0.1mol/L Ce(NO3)3 solution was put into 100ml mixed solution containing 0.1mol/L Ni(NO3)2 and 0.2mol/L Co(NO3)2, the obtained electrode would show the highest electrocatalytic activity.2. The definite KOH solution was put into the mixed solution containing 0.1mol/L Ni(NO3)2 and 0.2mol/L Co(NO3)2 to make Ni2+ and Co2+ convert into Ni(OH)2 and Co(OH)2 deposits completely. After the other ions were filtrated, the definite ammonia was put into the deposits to make them dissolve and form solution. Then the nickel foam/Ni-Co-O compound oxides film electrode was prepararion by dipping-thermal decomposition. After the electrochemical test, it could be found that the electrode showed good catalytic activity. At 4000A/m2 current dentity, its polarization potential was 0.638V, which was 132mV lower than the nickel foam electrode and 103mV lower than the nickel foam/Ni-Co-O electrode prepared by thermal decomposition of Ni(NO3)2 and Co(NO3)2. The component of the compound oxides on the surface of the electrode was characterized with XRD method. The result showed that the mainly component of the compound oxides was NiCo2O4.The best experimental condition of preparing the electrode was as follows: C [Ni(NH 3) 6 ] (OH)2 was 0.1mol/L, C Co(OH)2 ? NH3 was 0.2mol/L; The times of dipping-thermal decomposition was seven. The thermal decomposition temperature was 300℃.3. The electrode for oxygen evolution reaction in the course of alkaline water electrolysis was prepared by thermal decomposition of acetates and nitrates. The conditions on the content of Ce3+, the temperature of thermal decomposition, the times of dipping-thermal decomposition were researched on the influence of the electrocatalytic activity of the electrodes. The results proved that the electrodes could display better catalytic activity when C Ni2+: C Ce3+: C Co2+=0.4:0.6:2. The times of dipping-thermal decomposition influenced the overlay degree and thickness of the film, thus influenced the electrocatalytic activity of the electrode. The steady state polarization curves and cyclic voltammetric curves of the electrodes could proved that seven times of dipping-thermal decomposition was the best when C Ni2+ was 0.06mol/L, C Ce3+ was 0.04mol/L, C Co2+ was 0.2mol/L. The temperature of thermal decomposition could influence the content of the compound oxides film, thus could influence its electrocatalytic activity. The electrochemical experiment showed that the obtained compound oxides film electrode could display the highest electrochemical activity when the temperature of thermal decomposition was 340℃. XRD results proved that the mainly components of the obtained compound oxides film were NiCo2O4 and CeO2. Because of the lower characteristic diffraction apices of the oxides on the chart, the compound oxides could be judged for the mixed oxides owning lower crystal degree. From the SEM pictures of the surfaces of the elecatrodes, it could be found that many raised particulates appeared on the surfaces of the electrodes after Ce element was introduced into the oxides, thus increased the microcosmic surface area of the electrodes greatly. The data of BET surface area about the oxides proved the results. Thus the electrocatalytic activity of the electrodes was improved greatly.By comparing the steady state polarization curves and cyclic voltammetric curves of the electrodes prepared with different solution, it could be found that acetates and Ce element were both the favourable factors to improve the electrochemical activity of the electrodes. The stability of the electrodes was tested in Tianjin Mainland Hydrogen Equipment Co. Ltd. After 100 hours’experiment, it could be found that the electrode not only had better catalytic activity but also had better stability. At the current density of 4000 A/m2, the water electrolysis cell voltage was only 1.93 V, which was about 250 mV lower than that of the compartment which used the nickel foam electrode as the anode.The best experimental condition of preparing the electrodes was as follows: 1. with the method of thermal decomposition of acetates. 2. C Ni2+: C Ce3+: C Co2+=0.4:0.6:2. 3. dipping-thermal decomposition seven times. 4. at the thermal decomposition temperature of 300℃.