Engineering Cobalt Defects in Cobalt Oxide for Highly Efficient Electrocatalytic Oxygen Evolution

Abstract

Defect engineering is an effective way to modulate the electric states and provide active sites for electrocatalytic reactions. However, most studied oxygen vacancies are unstable and susceptible under the oxygen circumstance. Here, we fabricated cobalt-defected Co 3−x O 4 in situ for an efficient oxygen evolution reaction (OER). XAFS and PALS characterizations show that the crystals have abundant Co vacancies and a distorted structure. DFT calculations indicate that the metal defects lead to obvious electronic delocalization, which enhances the carrier transport to participate in water-splitting reactions along the defective conducting channels and the water adsorption/activation on the catalyst surface. Therefore, cobalt-defected Co 3−x O 4 shows remarkably high OER activity by delivering a much lower overpotential of 268 mV@ 10 mA cm −2 (with a small Tafel slope of 38.2 mV/dec) for OER in KOH electrolyte, in comparison with normal Co 3 O 4 (376 mV), IrO 2 (340 mV), and RuO 2 (276 mV). This work opens up a promising approach to construct electronic delocalization structures in metal oxides for high-performance electrochemical catalysts.

Laser Fragmentation‐Induced Defect‐Rich Cobalt Oxide Nanoparticles for Electrochemical Oxygen Evolution Reaction

“…Owing to the lower formation energy of Co 2+ defects than that of Co 3+ defects, Co 2+ defects are preferentially generated in a Co 3 O 4 spinel structure, matching well with the observation in this study. It has been well documented that introducing vacancies is favorable for both electrocatalytic activity and structural stability.…”

“…The formation of defects results in distortion to neighboring atoms and electronic delocalization. Such effects can enhance the charge transport in semiconductors and lower the adsorption energy of water molecules, respectively, which contribute to a higher electrocatalytic activity . Furthermore, the structure distortion helps to decrease the surface energy and hence endow the defective Co 3 O 4 with better structural stability …”

“…Moreover, theoretical calculations have revealed that tuning the electronic state of Co 3 O 4 modulates the adsorption energy of intermediate species to lower the energy barrier . This can be achieved by substitution of a foreign element (e.g., Ni, Cr, Cu), defect formation, and constructing hybrid structures . Despite the massive amount of work on developing cobalt oxide catalysts, there is still a challenge to fabricate cobalt oxide in a scalable system, which delivers nanoscale morphology with modified electrical structure for efficient OER catalysis.…”

A review of transition metal‐based bifunctional oxygen electrocatalysts

“…In addition, researchers have reported that many of these advanced materials potentially possess numerous interior defects and oxygen vacancies, allowing for the publication of many satisfactory findings. However, the vacancies of other metal or nonmetal elements or defects in nonoxide compounds have rarely been discussed . For example, graphyne is a star‐shaped material similar to graphene which can be considered to be a mixed hybridization of sp n in which 1 < n < 2.…”

Promoting Oxygen Evolution Reaction of Co‐Based Catalysts (Co3O4, CoS, CoP, and CoN) through Photothermal Effect

“…It is desirable to design low‐cost electrocatalysts to lower the required overpotentials for OER . Due to its Earth abundance, ecofriendliness, and attractive catalytic activity, Co 3 O 4 has been intensively investigated as an efficient water oxidation catalyst . However, it suffers from inherently poor electrical conductivity and sluggish kinetics, which make it less competitive as compared with other electrode materials.…”