Carbon aerogel and xerogel composites with polypyrrole as electrocatalysts for oxygen reduction reaction

Abstract

Due to their exceptional electrical conductivity and stability, carbon-based conductive polymer composites have attracted attention as non-platinum group metal (non-PGM) catalysts for the oxygen reduction reaction (ORR), a crucial reaction in electrochemical energy conversion. In this study, carbon aerogels (CA) and xerogels (CX, CXA) were first synthesized by sol-gel method under different drying conditions, including supercritical drying after solvent exchange of water with acetone (CA), drying under ambient conditions after solvent exchange of water with acetone (CXA), and drying directly under ambient conditions without solvent exchange of water with acetone (CX). Then, polypyrrole (PPy) composites were prepared by chemical polymerization over these carbon-based materials. Scanning and transmission electron microscopy with energy-dispersive X-ray spectroscopy and Raman spectroscopy were carried out on the synthesized CA, CXA, CX, and PPy composites. The electrochemical investigation of the synthesized materials reveals that they catalyze ORR mainly through two-electron reduction of molecular oxygen. The influence of the materials’ synthesis method, structure, and addition of PPy on their activity towards ORR was investigated. The best performance was observed for the CA2 catalyst, demonstrating the highest diffusion-limited current density, the lowest Tafel slope, the highest value of the half-wave potential, and the highest number of exchanged electrons. Furthermore, this material showed good stability during the long-term chronoamperometric study, making it a promising material for long-standing ORR catalysis.