Synergistic Electrocatalysts Impact Efficient and Durable Oxygen Evolution Catalysis for Proton Exchange Membrane Water Splitting
Authors: Chong Lina , Ding Wenjiang 
Published: August 2024

Low-temperature water electrolysis can rapidly produce environmentally sustainable or green hydrogen, and is a prospective means of storing energy from renewable but intermittent power sources, such as wind and solar, in future clean energy infrastructure (1-4). Commercial water electrolysis either use liquid alkaline electrolyte or proton exchange membrane electrolyte (1). The proton exchange membrane water electrolysis (PEMWE) offers more advantages than the alkaline counterpart, such as higher purity of H2, lower resistance losses, more compact design, and what the most important is the compatible with the intermittent of the renewable energy (1-2). The grant challenge remaining in PEMWE is the development of the highly active, cost effective and stable catalysts for oxygen evolution reaction (OER), which is very sluggish requiring large amounts of precious metal as the catalysts, such as Ir, Ru and their oxides (1).

In PEM water electrolysis cells, the catalysts should have high surface areas and high porosities that exposit sufficient active sites available to the reactants and electrolyte, as well as transferring the bubble out of the catalyst surface to ensure a fast mass transfer (5). Also, the OER is dependent on the inherent conductivity of the catalysts or the supports (1). For example, poor electronic conductivity within the catalyst layer will result in poor lateral conductivity across the catalyst layer, thus catalyst not in the vicinity of the porous transport layer will not participate in the reaction. To enable the widespread penetration of the PEMWE technologies, it is urgently to reduce the Ir loading to the sustainable level (~ 0.3 mg/cm2) compared with the current commercial usage (2-6 mg/cm2). Alternatively, to develop precious metal free catalyst with high efficiency and sustained durability (5).

In this presentation, we will describe a method of preparing highly active yet stable synergistic electrocatalysts for oxygen evolution reaction for PEMWE. The new catalysts contain IrCoOx/ RuCoOx cluster and La&Li co-doped Co3O4 fiber which was derived from cobalt zeolitic imidazolate framework as precursor. The OER activities of the catalysts were first tested in O2 saturated acidic electrolyte by ring disk electrode (RDE), which displayed high mass activity 26-50 times that of commercial Ir and RuO2. The catalysts were fabricated into membrane electrode assemble and measured under real PEM water electrolysis condition. The cells demonstrated 2 A/cm2@1.76 V @0.25 ± 0.05 mgIr/cm2 loading, and negligible degradation after ~250 h chronoamperometric measurements at 2 A/cm2 (6), which meets the target set by US DOE for OER catalysts for PEMWE.

The characterizations of the fresh and post-electrochemical samples were investigated by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), X-ray absorption near-edge structure (XANES), extended X-ray absorption fine structure (EXAFS), transmission electron microscopy (TEM), Raman spectroscopy and BET surface analysis. We also performed DFT simulation on the OER reaction pathways over Ir and Co sites of different facets parallelly on basis of the TEM results. The result reveals the synergy between Ir/Ru and Co resulting in the enhanced catalytic activities of both IrCoOx /RuCoOx and LaLi@Co3O4 toward OER.

Acknowledgments:

This work was supported by Overseas Outstanding Youth Fund project, shanghai Jiao Tong university, Shanghai, China; Shanghai Pujiang talent Plan, Shanghai, China; Argonne National Laboratory through Maria Goeppert Mayer Fellowship, US; State Key Laboratory of Metal Matrix Composites, shanghai Jiao Tong university, Shanghai, China. The works performed at Hydrogen research center, shanghai Jiao Tong university, and Argonne National Laboratory’s Center for Nanoscale Materials and Advanced Photo Source.

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