Synthesis And Electrochemical Properties Of Ir-based Catalysts For Oxygen Evolution Reaction

Efficient, low-cost anode oxygen evolution reaction (OER) catalyst is the key to the development of the current water electrolysis technology. The best catalysts for OER are the precious metal oxides, such as RuO2and IrO2, and IrO2has better stability. This paper has designed and prepared a series nanostructure Ir-based electrocatalysts for OER proceeding from the improvement of the IrO2catalyst utilization to reduce the amount of it. The main contents and results are summarized as follows,1. Nano IrO2catalyst and its size effectNanosized IrO2powder with rutile structure was prepared by the combination of colloidal and high-temperature air annealing methods. Comparing their OER catalytic activity, it is found that the grain size and OER activity of the IrO2increase, the voltammetry charges drop and the intrinsic activity increase firstly and then decrease with the increasing of heat treated temperature. The IrO2which was annealed at550℃has the best intrinsic activity.2. Three dimensional ordered macroporous (3-DOM) IrO2catalyst3-DOM IrO2was prepared by SiO2colloidal crystal template and the effect of heat treatment temperature on the morphology and performance was also observed. The prepared3-DOM IrO2material also has the rutile structure and the hierarchical pore structure. The cross-linked primary macropores are about300nm with～8nm mesopores on their walls. As compared with colloidal IrO2, the BET surface area and the electrochemical active surface area of the3-DOM IrO2increased approximately2-fold and1.4-fold, respectively, and OER catalytic activity increased by about1.5times. It is found that the electrochemical active area and the OER activity decrease with increasing temperature. When the heat treatment temperature exceeds700℃, the macroporous structure of the material loss and the mesopores also disappear in the meanwhile.3. The transition metal (Co, Ni)-doped and surface Ir-rich binary oxides catalysts for OERA series of Ir1-xNixO2-y and Ir1-xCoxO2-y oxides were prepared by pyrolysis method. When the doping content is less than0.3, the materials maintain a single rutile structure. With xNi increases, the electrochemical active surface areas of the Ir1-xNixO1-y catalyst reduce. The addition of the Co oxides (xCo<0.66) can improve the dispersion of the IrO2. The catalytical activity of the Ir0.7Ni0.302-y catalyst is the best. While the OER catalyst activity of Ir1-xCoxO2-y, even when xCo up to0.724, can still comparable to pyrolysis IrO2.The sub-phase components in the composite oxides can be removed by pickling process. After pickling, the content of non-noble metal in the oxides are xNi=0.34and xco=0.31, respectively, which are consistent with the contents of Ni or Co in the doped oxides prepared by pyrolysis method. The resulting materials after pickling are the surface Ir-rich structures and have mesoporous with different sizes. The electrochemical areas of the Iro.66Nio.34O2-y and Iro.69Co0.31O2-y catalysts synthesized by pickling method are3.1times and2.1times as high as the Ni or Co doped oxides prepared by pyrolysis method with similar composition, respevtively. Their OER activities are increased, while the stabilities have been improved greatly.4. The lrO2/Nb-doped TiO2catalystThe Ti0.95Nb0.05O2nanoparticles were synthesized by sol-gel method with a BET surface area of82.6m2.g-1and contained mesoporous structure. The supported IrO2was prepared by thermal decomposition method, Adams melt method and colloidal method respectively. It is found that the IrO2/Ti0.95Nb0.05O2catalyst prepared by colloidal method has the best mass activity and the area activity. The voltammetry charges and OER activity increase with IrO2wt%increases. When IrO2wt%is up to33%, the apparent activity is close to the non-carrier IrO2nanoparticles. When IrO2wt%is more than22%, the mass activity is higher than the non-carrier IrO2catalyst. As the IrO2wt%increased to26%, its mass activity has almost reached the optimum value, the IrO2nanoparticles uniformly disperse on Ti0.95Nb0.05O2surface and loading IrO2has higher stability than no-carried IrO2.