(Invited) Electrochemical Construction of 3-D Catalyst Layer on Ordered Liquid-Gas Diffusion Electrode for Highly Stable and Cost-Efficient PEM Water Electrolyser

Abstract

Proton exchange membrane (PEM) water electrolyser is an ideal way to produce green hydrogen with intermittent renewable energy. The high cost of noble metal in membrane electrode assembly is one of the key problems to be solved for its commercial applications. Developing 3-D electrode with high utilization of noble metal and prominent performance of mass diffusion is a promising solution.In this work, titanium foil with ordered openings is applied as liquid-gas diffusion layer (LGDL) for anode by photolithography. And 3-Dimensional structural catalyst layer (CL) is coated by controlled pulse electrodeposition. By adjusting the concentration of electrolyte, current density and pulse parameter, catalyst layer with structure of nanowires, nano-urchin and nano-flower can be obtained. With medium current density of 5 mA/cm2, a structure variation from nanowire to nano-urchin could be observed by prolonging the electrodepositing time. While high current density of 20 mA/cm2 was applied, catalyst layer with nano-flower structure was formed. However, similar morphology could not be observed when a flat titanium foil was used as substrate. The controlling mechanism would be studied with scanning electrochemical microscopy to unveil the key controlling issue, such as distribution of local current and steric effect of released gas. The single cell performance with nano-urchin CL coated ordered LGDL as anode electrode was studied. Though coverage of anode electrocatalyst on PEM is only 45% as the porosity of order LGDL is 55%, the single cell performs excellent activity and stability due to the high surface area, enhanced mass diffusion and structural stability of 3-D CL. With optimized loading of 0.25 mgIr /cm2, initial performance of 1.795 V@ 1 A/cm2 can be obtained. And a prominent performance on stability with decay rate of 4.17 μV/h is shown after 4000h running under 1A/cm2 at 80 ℃. It is predictable that, by further adjusting the pore diameter and porosity of order LGDL to optimize the area of electrocatalyst/membrane interface and mass diffusion, the performance could be further improved to fulfill long-term operation under high current density (＞2A/cm2). Figure 1