Synthesis, Microstructure Control And Performance Study Of Electro-catalysis Composite Materials In Proton Exchange Membrane Water Electrolysis

Proton exchange membrane (PEM) water electrolysis has been considered as the optimal selection of the harmonious development of the energy and enviroment in the future due to certain advantages, such as higher efficiency, higher purity, and better safety and reliability, and thus can be used as the energy storage and conversion devices combining with solar power and wind power generation. However, the poor reversibility and slow reaction kinetics of electro catalytic materials, the deficiency of microstructure and multiple interfaces confine the industrialization process serviously. Therefore, it is necessary to develop high performance and low price catalyst to reduce the reaction kinetics loss.The objective of the thesis was the enhancement of the activity of oxygen evolution reaction (OER) catalyst and hydrogen evolution reaction (HER) catalyst as well as the utilization ratio of the noble catalysts. From the point of view of material and microstructure. the electron and proton transport, gas and water transport of the catalyst and catalyst layer were optimized. The main work was divided into three parts:(1) The synthesis teconology of support materials with different composition and controlled microstructure were developed by the use of composite support. The effect on the catalystic activity of the interactive support effect between the support materials and the active phase were also investigated. From the point of view of material composition, composite materials consisting of antimony doped tin oxide and Cs-substituted phosphotungstate were synthesized as the support of iridium oxide. The composite support possessed functionality of mixed electronic and protonic conductivity with independently distributed nanosphere structure. The effect of catalyst supports on the catalytic activity of IrO2 might be the better dispersion of iridium oxide particles. more establishments of electrocatalystic sites and increase of the protonic conductivity of the catalyst layer. From the point of view of microstructure. electrospinning method combining with the calcine process was employed to fabricate antimony doped tin oxide porous nanowire. Comparing with the nanoparticles support, the characteristic nanowire structure and the fabricated pore structure of the support were expected to promote the charge transport and gas-liquid transport in the catalyst layer. With the supported catalysts, the cell voltages were 60 mV and 100mV lower than that of pure IrO2 at 80℃ and 2 A cm-2.(2) Aiming at decreasing the ohmic loss and the polarization loss, a novel CCM embedded with Cs1.5HPA in the skeleton of the Nafion(?) ionomer and the Nafion(?) membrane was prepared and possessed functionality of improved protonic conductivity. Meanwhile, the ionomer content in the catalyst layers was further optimized. The optimal mass ratio of anodic catalyst and the ionomer was 9:1. Thus obtained CCM exhibited the best water electrolysis performance and the terminal voltage of the electrolysis cell was 1.59 V at a current density of 2 A cm-2 and 80℃.(3) Firstly, highly dispersed amorphous Ni-P catalysts were synthetized and then were calcined at 300℃ to obtain the multi-phase crystalline Ni-P catalysts. The phase composition, crystal structure and particle size effected on the activity of the above catalysts were investigated. To achieve the current density at 20 mA cm-2, the overpotential of the armorphous Ni-P catalysts was 262 mV vs NHE. While, it required a lower overpotential of 154 mV vs NHE for the crystalline Ni-P catalysts, which showed improved catalystic activity (with crystalline Ni-P loading of 2 mg cm-2). Furthermore, an armorphous Ni-P alloy coat (with Ni-P alloy loading of 10 mg cm-2) was prepared on the stainless steel felt substrate with electroless plating method. At 20 mA cm-2, the overpotential of the Ni-P alloy coat was 224 mV vs NHE. The Ni-P alloy coated felt was directly used as a HER electrode in the electrolysis cell. At 80℃ and 500 mA cm-2, and the terminal voltage was 2.06 V (with the anodic catalyst loading of 1.5 mg cm-2).