In Situ Identification and Time-Resolved Observation of the Interfacial State and Reactive Intermediates on a Cobalt Oxide Nanocatalyst for the Oxygen Evolution Reaction

Abstract

Cobalt oxide (assigned as CoO x ) is an efficient oxygen evolution reaction (OER) nanocatalyst, which has been extensively studied as a replacement to noble metal-based catalysts. The recent observations and understandings for the interfacial state, adsorbed intermediate products, and rate-determining steps (RDS) on CoO x , however, have remained elusive because of the dynamic transformation of different Co ions and the transient nature of the intermediates formed during the OER process. In this work, we propose that under the chosen experimental conditions, the redox process between Co­(III) and Co­(IV) species does not follow a proton-coupled electron transfer mechanism that is thought to be common prior to the OER, but it involves a proton-decoupled electron transfer, clarified by isotope labeling experiments and in situ electrostatic modulation. The interfacial state of CoO x is negatively charged prior to the formation of Co­(IV)O species. The theoretical concentration of the resulting Co­(IV)O species is approximately 0.1229 × 1019 cm–2. The Co­(IV)O species are demonstrated to directly regulate the OER performance. Moreover, we experimentally monitor the dynamic evolution behaviors of Co­(IV)O, Co­(O)­O–, OOH*, and O2 –* intermediates during the OER with in situ time-resolved infrared spectroscopy, and the following elementary step OOH* + OH– → OO–* + H2O is likely to be the unexpected RDS in the OER process.

Speciation of Oxygen Functional Groups on the Carbon Support Controls the Electrocatalytic Activity of Cobalt Oxide Nanoparticles in the Oxygen Evolution Reaction

“…Furthermore, when a metal oxide phase is introduced, interactions of the material components will occur at their interface and may contribute to the formation of new active centers. It was recently shown that over CoO x catalyst, the third OER step is probably the rate-determining step, M-OOH + OH – → M-OO + H 2 O + e – . However, studies of cobalt oxyhydroxide (CoOOH) as the active phase led to the identification of the release of dioxygen from the superoxide intermediate (Co–O–O • –Co) as the rate-determining step of the OER (fourth step) .…”

Synergistic Effect in a Metal–Organic Framework Boosting the Electrochemical CO2 Overall Splitting

“…The designability makes it feasible to integrate different active sites into the same framework to achieve synergistic catalysis or a bifunction. Moreover, the catalytic performances and stabilities of some MOFs are close to those of the state-of-the-art materials (Cu(100) and Cu(100)/Cu(111) interface). , Metallic phthalocyaninates, especially nickel­(II) phthalocyaninate (PcNi), have been demonstrated to be excellent catalysts for the electroreduction of CO 2 to CO, − while cobalt oxides have shown remarkable OER activity. , Therefore, it should be an opportunity to achieve high-performance CO 2 overall splitting via the integration of the above two species into one catalytic system. In this work, we designed and synthesized a MOF with both PcNi sites and planar CoO 4 nodes (or active sites) and studied its performance as a bifunctional CO 2 RR/OER electrocatalyst for CO 2 overall splitting.…”

“…However, it is difficult to construct a catalyst with both high OER activity and high CO 2 RR activity. So far, overall water splitting and OER/oxygen reduction reaction (ORR) have attracted considerable attention, − ,− whereas CO 2 overall splitting has rarely been reported. Moreover, such bifunctional catalysts for CO 2 overall splitting showed very low current densities (0.2–12 mA cm –2 ), ,,− far below the commercial current density, which may be due to the poor activities of OER/CO 2 RR and/or the unmatched energy levels.…”

“…35,36 Metallic phthalocyaninates, especially nickel(II) phthalocyaninate (PcNi), have been demonstrated to be excellent catalysts for the electroreduction of CO 2 to CO, 37−39 while cobalt oxides have shown remarkable OER activity. 19,21 Therefore, it should be an opportunity to achieve high-performance CO 2 overall splitting via the integration of the above two species into one catalytic system. In this work, we designed and synthesized a MOF with both PcNi sites and planar CoO 4 nodes (or active sites) and studied its performance as a bifunctional CO 2 RR/OER electrocatalyst for CO 2 overall splitting.…”

Material Changes in Electrocatalysis: An In Situ/Operando Focus on the Dynamics of Cobalt‐Based Oxygen Reduction and Evolution Catalysts

“…[46] Interestingly, these transitions are partially reversible, resulting in a mixed Co(OH) À O À and Co 4 + =O surface species at OER potentials, demonstrating the importance of highly oxidized Co in the OER mechanism. [49] Electrodeposition is a facile, scalable, and tunable method to synthesize Co-based electrocatalysts. [50] The films produced via electrodeposition have been shown to start with average Co oxidation states between 2 + and 3 + and increase in oxidation state during OER.…”