Anion Resistant Oxygen Reduction Electrocatalyst in Phosphoric Acid Fuel Cell

Kara Strickland, Ryan Pavlicek, Elise Miner, Qingying Jia, Ivo Zoller, Shraboni Ghoshal, Wentao Liang, Sanjeev Mukerjee

Index: 10.1021/acscatal.8b00390

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Abstract

Phosphoric acid fuel cells are successfully used as energy conversion technologies in stationary power applications. However, decreased proton conductivity and lower oxygen permeability of phosphoric-acid-imbibed membranes require prohibitive loadings of the traditional noble-metal-based electrocatalyst, such as platinum supported on carbon. Additionally, specific adsorption of phosphate anions on the catalyst results in a surface poisoning that further reduces electrocatalytic activity. Here we report a nonplatinum group metal (non-PGM) electrocatalyst as an alternative cathode electrocatalyst for oxygen reduction in phosphoric acid fuel cells. The non-PGM was prepared in a one-pot synthesis using a metal organic framework and iron salt precursor. Phosphate anion poisoning was monitored electrochemically and spectroscopically in reference to the current state-of-the-art Pt-based catalyst at room temperature. Unlike Pt-based catalysts that are prone to phosphate poisoning, the non-PGM electrocatalyst exhibits immunity to surface poisoning by phosphate anions at room temperature. Imaging with microscopy reveals that the iron particles are isolated from the electrolyte by graphitic layers, which ultimately protect the iron from phosphate anion adsorption. The non-PGM electrocatalyst represents the highest performance to date in a high-temperature phosphoric acid membrane system, which is likely attributed to its immunity to phosphate adsorption at the harsher fuel cell environments.