Highly Efficient and Durable Electrocatalysis by a Molecular Catalyst with Long Alkoxyl Chains Immobilized on a Carbon Electrode for Water Oxidation

Abstract

A dinuclear Ru complex, proximal,proximal-[Ru2L­(C8Otpy)2(OH)­(OH2)]3+ (C8Otpy = 4′-octyloxy-2,2’; 6′,2″-terpyridine) (1) with long alkoxyl chains, was synthesized to be immobilized on a carbon paper (CP) electrode via hydrophobic interactions between the long alkoxyl chains and the CP surface. The 1/CP electrode demonstrated efficient electrocatalytic water oxidation with a low overpotential (ηonset) of 0.26 V (based on the onset potential for water oxidation) in an aqueous medium at pH 7.0, which is compared advantageously with those of hitherto-reported molecular anodes for water oxidation. The active species of RuIIIRuIII(μ-OO) with a μ-OO bridge was involved in water oxidation at 0.95 V versus Ag/AgCl. As the applied potential increased to 1.40 V, water oxidation was promoted by participation of the more active species of RuIIIRuIV(μ-OO), and very durable electrocatalysis was gained for more than 35 h without elution of 1 into the electrolyte solution. The introduced long alkoxyl chains act as a dual role of the linker of 1 on the CP surface and decrease the η value. Theoretical investigation provides insights into the O–O bond formation mechanism and the activity difference between RuIIIRuIII(μ-OO) and RuIIIRuIV(μ-OO) for electrocatalytic water oxidation.

Bifunctional and regenerable molecular electrode for water electrolysis at neutral pH

“…Yagi et al , recently reported 91% Faraday efficiency of oxygen evolution with the RuCP electrode {RuCP = immobilized proximal,proximal-[Ru 2 L(C 8 Otpy) 2 (OH)(OH 2 )] 3+ on carbon paper, where C 8 Otpy = 4′-octyloxy-2,2′; 6′,2′′-terpyridine and L = 5-phenyl-2,8-di(2-pyridyl)-1,9,10-anthyridine} for the first one hour of electrolysis at 2.01 V at pH 7. 20 The Faraday efficiency with RuCP electrode over the first 3 h decreases to 45% when the applied potential was decreased by 450 mV. In our study, when the CPE using RuPFCC was repeated at 1.81 V for 48 h a TON of >7.4 × 10 3 could be achieved.…”

“…S15 † octyloxy-2,2 ′ ; 6 ′ ,2 ′′ -terpyridine and L = 5-phenyl-2,8-di(2pyridyl)-1,9,10-anthyridine} for the rst one hour of electrolysis at 2.01 V at pH 7. 20 The Faraday efficiency with RuCP electrode over the rst 3 h decreases to 45% when the applied potential was decreased by 450 mV. In our study, when the CPE using RuPFCC was repeated at 1.81 V for 48 h a TON of >7.4 × This journal is © The Royal Society of Chemistry 2023 10 3 could be achieved.…”

“…Anchoring the catalyst onto a conductive solid surface through a suitable linker can improve both the stability and the overall reactivity, leading to the enhancement of the current density. 17,20…”

“…[15][16][17][18][19] Ruthenium-based complexes have so far shown the best performance in terms of turnover number (TON), turnover frequency (TOF), and overpotential. 17,[20][21][22] However, for commercial applications, further improvement of their stability, as well as strategies for catalyst regeneration are needed.…”

“…RuPFCC (ruthenium catalyst anchored onto PFCC) was designed to combine the electrocatalytic activity from the molecular counterpart (of 1), with the current density, and robust features of the conductive support. 9,17,[20][21][22]35,40 The pyridines were covalently attached to the carbon cloth separated by two -CH 2 units, to allow for optimal distances for electron transfer and charge recombination. 41…”