Boosting the Loading of Metal Single Atoms via a Bioconcentration Strategy

Increasing the mass loading of transition metal single atoms coordinated with nitrogen in carbon-based materials (M-N-C) is still challenging. Herein, inspired by the bioconcentration effect in the living body, a biochemistry strategy for the synthesis of Fe-N-C single atoms is demonstrated. Through introducing ferrous glycinate into the growth of fungus, the Fe atoms are bioconcentrated in hyphae. The highly dispersed Fe-N-C single atoms in hyphae-derived carbon fibers (labeled as Fe-N-C SA/HCF) are prepared by the pyrolysis of Fe-riched hyphae. In the bioconcentration process, the uptake of Fe ions by hyphae promotes the secretion of glutathione and ferritin, which provides additional coordination sites for Fe ions. Accordingly, the mass content of Fe in bioconcentrated Fe-N-C SA/HCF reaches 4.8%, which is 5.3 times larger than that of the sample prepared by the conventional pyrolysis process. The present bioconcentration strategy is further extended to the preparation of Co, Ni, and Mn single atoms. Owing to the high content of Fe-N-C single atoms, Fe-N-C SA/HCF shows the onset potential (E_onset ) of 0.931 V versus reversible hydrogen electrode (RHE) and half-wave potential (E_1/2 ) of 0.802 V versus RHE in oxygen reduction reaction measurements, which is comparable to the commercial Pt/C catalysts.