Ultrathin Iron‐Cobalt Oxide Nanosheets with Abundant Oxygen Vacancies for the Oxygen Evolution Reaction

Abstract

Electrochemical water splitting is a promising method for storing light/electrical energy in the form of H fuel; however, it is limited by the sluggish anodic oxygen evolution reaction (OER). To improve the accessibility of H production, it is necessary to develop an efficient OER catalyst with large surface area, abundant active sites, and good stability, through a low-cost fabrication route. Herein, a facile solution reduction method using NaBH as a reductant is developed to prepare iron-cobalt oxide nanosheets (Fe Co -ONSs) with a large specific surface area (up to 261.1 m g ), ultrathin thickness (1.2 nm), and, importantly, abundant oxygen vacancies. The mass activity of Fe Co -ONS measured at an overpotential of 350 mV reaches up to 54.9 A g , while its Tafel slope is 36.8 mV dec ; both of which are superior to those of commercial RuO , crystalline Fe Co -ONP, and most reported OER catalysts. The excellent OER catalytic activity of Fe Co -ONS can be attributed to its specific structure, e.g., ultrathin nanosheets that could facilitate mass diffusion/transport of OH ions and provide more active sites for OER catalysis, and oxygen vacancies that could improve electronic conductivity and facilitate adsorption of H O onto nearby Co sites.

A general ligand-assisted self-assembly approach to crystalline mesoporous metal oxides

“…Mesoporous Co 3 O 4 samples obtained at different temperatures were tested for the OER to confirm the optimal calcination temperature of the electrocatalysts. As shown in Figure S14 , which is superior to most previous reports on non-precious OER electrocatalysts in alkaline aqueous electrolytes (Table 1) [28][29][30][31][32] . For comparison, the Co 3 O 4 /Fe 3 O 4 (2:1) composite demands an overpotential of 494 mV to achieve a current density of 10 mA cm −2 , and no obvious current response is observed when the working electrode film is prepared by pure mesoporous Fe 3 O 4 ( Figure S15).…”

A Surfactant‐Free and Scalable General Strategy for Synthesizing Ultrathin Two‐Dimensional Metal–Organic Framework Nanosheets for the Oxygen Evolution Reaction

“…Herein, we report as urfactant-free strategy to use amorphous metal oxide nanosheets (M-ONS), such as the ultrathin iron-cobalt oxide nanosheets (FeCo-ONS, 1.2 nm), [29] as sacrificial templates to form the MOF-74 nanosheets (M-MNS) by confined ligand coordination. It is assumed that the controllable leaching of metal ions from M-ONS could be realized by acidic ligand solutions under hydrothermal conditions,and lead to the enrichment of metal ions on the M-ONS surface for coordination reaction.…”

Cross-Linked CoMoO4/rGO Nanosheets as Oxygen Reduction Catalyst

“…From the transmission electron microscope (TEM) pictures (Figure 1e,f), it can be evidently seen that CoMoO4 is deposited (darker areas in the TEM image) on the surface of rGO, indicating that CoMoO4/rGO composite has been synthesized. (Figure 2b) which are the active catalytic sites which can promote the ORR [33,34]. Particularly, the splitting doublets of Mo 3d 3/2 and Mo 3d 5/2 peaks at 231.9 and 235.2 eV could be observed in Mo 3d XPS (Figure 2c), and the region width is 3.3 eV (∆ Mo 3d).…”

“…On the other hand, the CoMoO4 doping of rGO hinders the aggregation of graphene, the CoMoO4 can disperse onto rGO which can expose more cobalt based active sites. The Co 2+ plays a crucial role in ORR catalytic process [33,34]. Thus, the CoMoO4/rGO composite exhibits more exposed and accessible active sites compared with the pristine CoMoO4.…”