Cobalt Electrocatalyst on Fluorine Doped Carbon Cloth – a Robust and Partially Regenerable Anode for Water Oxidation

Abstract

The low stability of the electrocatalysts at water oxidation (WO) conditions and the use of expensive noble metals have obstructed large-scale H 2 production from water. Herein, we report the electrocatalytic WO activity of a cobalt-containing, water-soluble molecular WO electrocatalyst [Co II (mcbp)(OH 2 )] (1) [mcbp 2À = 2,6-bis(1-methyl-4-(carboxylate)benzimidazol-2yl)pyridine] in homogeneous conditions (overpotential of 510 mV at pH 7 phosphate buffer) and after anchoring it on pyridine-modified fluorine-doped carbon cloth (PFCC). The formation of cobalt phosphate was identified only after 4 h continuous oxygen evolution in homogeneous conditions. Interestingly, a significant enhancement of the stability and WO activity (current density of 5.4 mA/cm 2 at 1.75 V) was observed for 1 after anchoring onto PFCC, resulting in a turnover (TO) of > 3.6 × 10 3 and average TOF of 0.05 s À 1 at 1.55 V (pH 7) over 20 h. A total TO of > 21 × 10 3 over 8 days was calculated. The electrode allowed regeneration of ~85 % of the WO activity electrochemically after 36 h of continuous oxygen evolution.

Bifunctional and regenerable molecular electrode for water electrolysis at neutral pH

“…The hydrogen detector confirmed the identity of the gas bubbles as H 2 throughout this process. In our previous work, we could not see any such gas bubbles around CoPFCCox while performing ERE process at −0.59 V and −0.79 V. 24 The production of H 2 at around −0.59 V is an additional characteristic of this ruthenium electrocatalyst anchored electrode, RuPFCC. Understanding that one of the major challenges on the way of producing H 2 at neutral pH and aqueous solution is still the lack of efficient electrodes for HER, a series of new experiments using RuPFCC as cathode at the pH 7 phosphate buffer solution were carried out.…”

“…Envisioning that the prolonged oxidation might be a reason for partial deactivation and looking at the exciting electrochemical behaviour of RuPFCC in the negative potentials (Fig. 4d), we performed a CPE experiment at –0.59 V (see ESI†) for 60 min after the 8 h CPE at +1.71 V. 24 This reduction recovered the potential of WO. The next CPE at +1.71 V using the regenerated electrode as anode showed as high as 98% of the current density for the first 1k seconds (Fig.…”

“…Fluorine-doped carbon cloth (FCC) has been reported and recently tested by us a as robust and durable conductive support that allows for straightforward structural modication and catalyst graing. 23,24 We recently reported the preparation of CoPFCC electrode consisting of {Co II (mcbp)(H 2 O)} anchored onto pyridine-modied FCC, which showed high stability and robust features under WO conditions. 24 However, to enable sustainable production of H 2 from water, further improvement of overpotential and TO (turnover) values is needed.…”

Cerium Oxide on a Fluorinated Carbon-Based Electrode as a Promising Catalyst for Hypochlorite Production

“…ACC was the working electrode, and a graphite foil was used as the counter electrode. An external potential of 10 V was applied for 15 min as described in detail elsewhere . Cerium oxide was prepared by a hydrothermal process following a method described in the literature with slight modifications .…”

“…An external potential of 10 V was applied for 15 min as described in detail elsewhere. 33 Cerium oxide was prepared by a hydrothermal process following a method described in the literature with slight modifications. 34 In brief, equimolar (1 M) volumes of cerium chloride (CeCl 2 ) and citric acid (C 6 H 8 O 7 ) were mixed in an aqueous solution, where CeCl 2 acts as the oxide precursor, and citric acid plays the role of a capping agent stabilizing the particles during its germination and growth.…”