Phosphate-Tolerant Oxygen Reduction Catalysts

Abstract

Increased oxygen reduction reaction (ORR) kinetics, improved CO tolerance, and more efficient water and heat management represent significant advantages that high-temperature polymer electrolyte fuel cells (HT-PEFCs) operating with a phosphoric acid-doped polybenzimidazole (PBI) membrane offer over traditional Nafion-based, low-temperature PEFCs. However, before such HT-PEFCs become viable, the detrimental effect of phosphate chemisorption on the performance of state-of-the-art Ptbased cathode catalysts needs to be addressed. In this study, we propose a solution to the severe poisoning of Pt-based PEFC cathode catalysts with phosphates (H 2 PO 4 − and HPO 4 2−) by replacing standard Pt/C catalysts with phosphate-tolerant, nonprecious metal catalyst (NPMC) formulations. Catalysts with a very high surface area (845 m 2 g −1 ) were synthesized in this work from polyaniline (PANI), iron, and carbon using a high-temperature approach. The effects of metal precursors and metal loading on the morphology, structure, and ORR activity of the NPMCs were systematically studied. Electrochemical measurements indicated that as-prepared Fe-based catalysts (PANI-Fe-C) can tolerate phosphate ions at high concentrations and deliver ORR performance in 5.0 M H 3 PO 4 that is superior to that of Pt/C catalysts. A 30 wt % Fe-derived catalyst was found to have the most porous morphology and the highest surface area among studied Fe-based catalysts, which correlates with the highest ORR activity of that catalyst. These cost-effective and well-performing ORR catalysts can potentially replace Pt/C catalysts in phosphoric acid-based HT-PEFCs.

Engineering Favorable Morphology and Structure of Fe‐N‐C Oxygen‐Reduction Catalysts through Tuning of Nitrogen/Carbon Precursors

“…In particular, with respect to the individual precursor, PANI is graphitized into thin‐sheet assembled structures containing dominant micro/mesopores, which is in agreement with the measured high BET surface areas (1076 m 2 g −1 ). These large pores are due to in situ‐formed FeS being leached during the acid treatment, leaving behind such unique open pores . DCDA resulted in a completely different morphology wherein larger carbon particles are surrounded by highly graphitized nanosheets and nanoshells.…”

Atomically Dispersed Fe‐Nx/C Electrocatalyst Boosts Oxygen Catalysis via a New Metal‐Organic Polymer Supramolecule Strategy

“…[8][9][10] Among various non-PGM ORR catalysts developed in last decade, transition metalnitrogen-carbon (M-N-C) catalysts with M-N x coordination active sites embedded in the basal planes of carbon matrixes were the most promising ones due to their decent activity in both acidic and alkaline media and ease of scale-up production. [21,22] Generally, the M-N-C catalysts are prepared via high-temperature (T > 800 °C) pyrolysis process of transition metal (e.g., Fe, Co, Ni), nitrogen, and carbon precursors, during which the metal atoms are very easy to agglomerate into large particles. [21,22] Generally, the M-N-C catalysts are prepared via high-temperature (T > 800 °C) pyrolysis process of transition metal (e.g., Fe, Co, Ni), nitrogen, and carbon precursors, during which the metal atoms are very easy to agglomerate into large particles.…”

Nitrogen/Cobalt Co‐doped Mesoporous Carbon Microspheres Derived from Amorphous Metal‐Organic Frameworks as a Catalyst for the Oxygen Reduction Reaction in Both Alkaline and Acidic Electrolytes

“…[63] The study motive is due to the fact that H 3 PO 4 -based fuel cells (PAFCs) have been demonstrated to be tolerant to CO at a high level (3 %), thus dispensing with the complicated processes of CO removal in hydrogen fuel that was produced by the hydrocarbons reforming. [63] The study motive is due to the fact that H 3 PO 4 -based fuel cells (PAFCs) have been demonstrated to be tolerant to CO at a high level (3 %), thus dispensing with the complicated processes of CO removal in hydrogen fuel that was produced by the hydrocarbons reforming.…”