Harnessing the Extracellular Electron Transfer Capability of Geobacter sulfurreducens for Ambient Synthesis of Stable Bifunctional Single‐Atom Electrocatalyst for Water Splitting

Abstract

Single-atom metal (SA-M) catalysts with high dispersion of active metal sites allow maximum atomic utilization. Conventional synthesis of SA-M catalysts involves high-temperature treatments, leading to low yield with a random distribution of atoms. Herein, a nature-based facile method to synthesize SA-M catalysts (M = Fe, Ir, Pt, Ru, Cu, or Pd) in a single step at ambient temperature, using the extracellular electron transfer capability of Geobacter sulfurreducens (GS), is presented. Interestingly, the SA-M is coordinated to three nitrogen atoms adopting an MN 3 on the surface of GS. Dry samples of SA-Ir@GS without further heat treatment show exceptionally high activity for oxygen evolution reaction when compared to benchmark IrO 2 catalyst and comparable hydrogen evolution reaction activity to commercial 10 wt% Pt/C. The SA-Ir@GS exhibits the best water-splitting performance compared to other SA-M@GS, showing a low applied potential of 1.65 V to achieve 10 mA cm −2 in 1.0 M KOH with cycling over 5 h. The density functional calculations reveal that the large adsorption energy of H 2 O and moderate adsorption energies of reactants and reaction intermediates for SA-Ir@GS favorably improve its activity. This synthesis method at room temperature provides a versatile platform for the preparation of SA-M catalysts for various applications by merely altering the metal precursors.

Recent Developments of Microenvironment Engineering of Single‐Atom Catalysts for Oxygen Reduction toward Desired Activity and Selectivity

“…In recent years, Fe-N-C SACs exhibited a comparable catalytic property for ORR as compared to Pt, hence, the ORR mechanism on Pt (111) is quoted to on isolated atomic site. As shown in Figure 1a, Nørskov and coworkers viewed O 2 adsorption on Pt (111) as a chemical process, and they suggested ORR mechanism on Pt (111) only refers to *OOH, *O, and *OH intermediates. [97] Such O 2 → *OOH → *O→ *OH → H 2 O mechanism has been recognized by many researchers, such mechanism was referenced to reveal ORR pathway on metal center of SACs.…”

“…Particularly, when many SAAS are beneficial to OH departure, the formation of *OOH may be considered as the RDS, and the whole ORR pathway with O 2 adsorption is exhibited in Figure 1d. [121][122][123][124][125] Furthermore, previous researchers found that theoretical onset potential (E onset ) of Fe-N-C SACs usually smaller than that of Pt (111). To further figure out the ORR mechanism, Yuan et al found that the first O 2 molecule always occupies one sides of the planar active site to form the stable M-O 2 structure.…”

“…[97] Such O 2 → *OOH → *O→ *OH → H 2 O mechanism has been recognized by many researchers, such mechanism was referenced to reveal ORR pathway on metal center of SACs. [41,[104][105][106][107][108][109][110][111][112] Notably, for most of Fe-N-C SACs, DFT-calculated free-energy diagrams indicated that the dissociation of OH on metal center of SACs is the most endothermic elementary reaction. [104,113,114] Reducing adsorption strength of OH on metal center is considered to be the most direct mean to improve ORR performance.…”

“…[98][99][100][101][102][103] Therefore, the overwhelming researches about the specific ORR pathway mainly rely on DFT calculations. In recent years, Fe-N-C SACs exhibited a comparable catalytic property for ORR as compared to Pt, hence, the ORR mechanism on Pt (111) is quoted to on isolated atomic site. As shown in Figure 1a, Nørskov and coworkers viewed O 2 adsorption on Pt (111) as a chemical process, and they suggested ORR mechanism on Pt (111) only refers to *OOH, *O, and *OH intermediates.…”

“…Figure 1. a) DFT-calculated 4e − ORR on Pt(111) with *OOH, *O, and *OH intermediates. Reproduced with permission [97].…”