Modifying redox properties and local bonding of Co3O4 by CeO2 enhances oxygen evolution catalysis in acid

Abstract

Developing efficient and stable earth-abundant electrocatalysts for acidic oxygen evolution reaction is the bottleneck for water splitting using proton exchange membrane electrolyzers. Here, we show that nanocrystalline CeO2 in a Co3O4/CeO2 nanocomposite can modify the redox properties of Co3O4 and enhances its intrinsic oxygen evolution reaction activity, and combine electrochemical and structural characterizations including kinetic isotope effect, pH- and temperature-dependence, in situ Raman and ex situ X-ray absorption spectroscopy analyses to understand the origin. The local bonding environment of Co3O4 can be modified after the introduction of nanocrystalline CeO2, which allows the CoIII species to be easily oxidized into catalytically active CoIV species, bypassing the potential-determining surface reconstruction process. Co3O4/CeO2 displays a comparable stability to Co3O4 thus breaks the activity/stability tradeoff. This work not only establishes an efficient earth-abundant catalysts for acidic oxygen evolution reaction, but also provides strategies for designing more active catalysts for other reactions.

Advances in Oxygen Evolution Electrocatalysts for Proton Exchange Membrane Water Electrolyzers

“…Besides intrinsic chemical properties, interface engineering has been taken to enhance stability. [ 226,227 ] The distinctive carbon‐coated Co 3 O 4 nanoarrays are highly active and acid‐durable for oxygen evolution with a small overpotential (370 mV) to reach 10 mA cm −2 and exhibit a lifetime long for 86.8 h at a constant current density of 100 mA cm −2 ( Figure 13 a,b). [ 67 ] It is demonstrated that in situ‐formed amorphous carbon by pyrolysis of glucose provides a mechanical supporting layer to hinder exfoliation of catalysts, engendering significantly improved stability even though mass transfer might be slightly influenced by the layered coating.…”

Electrocatalytic acidic oxygen evolution reaction: From nanocrystals to single atoms

“…[99] Co 3 O 4 nanowire arrays with Ag doped on FTO substrate also sustained OER activity by 1.91 V with onset potential of current density 10 mA/cm 2 and exhibited high stability at overpotential of 370 mV for 10 h. [100] Studies have found that the introduction of CeO 2 nanocrystals can also improve the intrinsic catalytic activity of Co 3 O 4 . [101] Through the in situ Raman and ex situ XAS structure characterization of the Co 3 O 4 /CeO 2 catalyst before and after the OER test (Figure 5E,F), it was found that the introduction of CeO 2 changed the electronic structure of Co 3 O 4 and created a more favorable local bonding envi-ronment for Co 3 O 4 . Co 3 O 4 surface species are easily oxidized to OER active Co IV species, and the charge accumulation of Co 3 O 4 is inhibited under electrochemical conditions, which is the key to reducing the pre-redox of Co 3 O 4 in the acidic OER, and effectively promotes the massive remodeling of the catalyst surface, thereby improving the acidic OER activity.…”

“…(F) In situ Raman spectra of Co 3 O 4 (left panel) and Co 3 O 4 /CeO 2 (right panel) at various constant potentials (vs. RHE) without iR correction (increased from 1.22 to 1.87 V and then back to 1.22 V). Reproduced with permission: Copyright 2021, Nature Publishing Group [101] Tafel slope, without dependence on proton concentration. [97] γ-MnO 2 showed OER performance at a current density of 10 mA/cm 2 with overpotential of 428 mV in acidic media, and by doping with TiO 2 its stability was further improved (Figure 5B,C).…”

The Pivotal Role of s‐, p‐, and f‐Block Metals in Water Electrolysis: Status Quo and Perspectives

“…[181] These enhancement mechanisms can also be applied to several systems, such as NNTM sulfide, [183] phosphide, [184] high entropy oxide, [185] and metal-organic framework. [186] Apart from the aforementioned function, rare-earth metals also display some other attractive functions: [71,[187][188][189][190][191][192][193][194][195] i) alloying with other NNTMs to form the newly structured intermetallics with high conductivity, ii) binding with anions to serve as a confinement substrate to anchor the single metal atom, and iii) taking rare-earth element oxides or hydroxides as the coupling subunit to build heterointerfaces. On the basis of the Brewer-Engel theory, [187] alloying the NNTMs that have empty or half-filled vacant d orbitals with rare-earth metals with empty and vacant d orbitals is a viable strategy to design the advanced electrocatalysts for HER.…”