Water Oxidation Electrocatalysis with a Cobalt‐Borate‐Based Hybrid System under Neutral Conditions

Abstract

The development of new water oxidation electrocatalysts that are both stable and efficient, particularly in neutral conditions, holds great promise for overall water splitting. In this study, the electrocatalytic water oxidation performance of a new cobalt-based catalyst, Co (BO ) , with a Kotoite-type crystal structure is investigated under neutral conditions. The catalyst is also hybridized with CNTs to enhance its electrocatalytic properties. A remarkable increase in catalytic current along with a significant shift in the onset overpotential is observed in Co (BO ) @CNT. Additionally, CNT addition also greatly influences the surface concentration of the catalyst: 12.7 nmol cm for Co (BO ) @CNT compared with 3.9 nmol cm for Co (BO ) . Co (BO ) @CNT demands overpotentials of 303 and 487 mV to attain current densities of 1 and 10 mA cm , respectively, at pH 7. Electrochemical and characterization studies performed over varying pH conditions reveal that the catalyst retains its stability over a pH range of 3-14. Multi-reference quantum chemical calculations are performed to study the nature of the active cobalt sites and the effect of boron atoms on the activity of the cobalt ions.

A Noble‐Metal‐Free Heterogeneous Photosensitizer‐Relay Catalyst Triad That Catalyzes Water Oxidation under Visible Light

“…[26,36] The reactivity parameters in the current study suggest asimilar Co centered O À Ob ond formation under photocatalytic conditions.M oreover,[ Fe-TPyP] moiety in the [CoFe-TPyP] system is presumably the photochemically active species and the role of the Co centers is similar to what we have previously reported. [26,36] The reactivity parameters in the current study suggest asimilar Co centered O À Ob ond formation under photocatalytic conditions.M oreover,[ Fe-TPyP] moiety in the [CoFe-TPyP] system is presumably the photochemically active species and the role of the Co centers is similar to what we have previously reported.…”

Hydrothermally Synthesized Cobalt Borophosphate as an Electrocatalyst for Water Oxidation in the pH Range from 7 to 14

“…CoBP exhibits Co2p 3/2 signal at around 781 eV and Co2p 1/2 signal at around 796 eV, respectively (Figure a). Additionally, broad and distinguishable satellite signals were also observed at around 786 eV and 803 eV respectively, which correspond to Co 2+ . O1s (Figure b), B1s (Figure c) and P2p (Figure d) signals were observed at 531.7 eV, 191 eV and 134 eV, respectively.…”

“…TOF has been extracted from Tafel plots and aforementioned surface concentration data according to the following equation (Eq. 2), where j is the current density obtained from CA measurement at certain overpotential, A is the area of the electrode, 4 indicates the mole of electrons consumed for evolving one mole of O 2 from water, F is Faraday's constant and m is the number of moles for active sites …”

“…These studies reveal that amorphous metal borate systems are promising oxygen evolution electrocatalyst. Conversely, Karadas et al; reported the first crystalline metal borate catalyst Co 3 (BO 3 ) 2 with a well‐known Kotoite‐type crystal structure and its hybrid with multi‐walled CNTs, Co 3 (BO 3 ) 2 @CNT …”

“…Recently, cobalt and nickel containing catalysts that are prepared by electrodeposition of metals salts in the presence of phosphate (Pi) and borate (Bi) electrolyte have been reported as an important class of efficient earth‐abundant electrocatalysts . Two different types of strategies have been employed to formulate borate based electrocatalysts; 1) in which borate groups act as co‐anions in the formation of layered metal oxides, 2) in which borate groups are directly coordinated to metal ions to prepare metal borate (M−Bi) . For this purpose, either BH 4 − , a reducing agent, is used as the boron source or metal‐based films (CoS 2 , CoSe 2 , CoFe 2 O 4 , CoP) are electrochemically treated in the borate buffer solution to assist borate formation in the structure .…”