Carboxylate-assisted Fe-based bimetallic oxygen reduction catalysts for coulomb electrolytic oxygen sensors

High-efficiency oxygen reduction electrocatalysts is crucial for low-carbon development. Iron-nitrogen co-doped carbon materials (Fe-N-C) prepared from ZIF-8 are well recognized for their remarkable potential to enhance ORR reaction rates. However, the challenge of limited and singular active sites due to insufficient metal loading has impeded the progress of Fe-N-C-based materials. In this paper, the above-mentioned problems were alleviated by introducing a second transition metal (Co, Mn, Zr) to form a bimetallic catalyst with Fe. Carboxylates are also introduced for assistance to generate one-dimensionally entangled carbon nanotubes, then the material can perform charge transfer better. In the alkaline medium, the half-wave potential of FeCo-N-C-OAc synthesized with carboxylate added reached 0.907 V, FeMn-N-C-OAc was 0.893 V, and FeZr-N-C-OAc was 0.892 V, which was improved compared with the samples without carboxylate added. In the range of 100–1000 ppm oxygen concentration, the oxygen sensors based on three catalysts that with carboxylate added showed good linearity and high response currents, especially FeMn-N-C-OAc showed an average response time of 53 s and a relative current fluctuation of only 4 % after 28 days. When improving the performance of Fe-N-C-based catalysts used in coulometric electrolytic oxygen sensors, this work can be regarded as a new strategy.