Aqueous Electrochemical Partial Oxidation of Gaseous Ethylbenzene by a Ru-Modified Covalent Triazine Framework

Abstract

Aqueous electrochemical oxidation of hydrocarbons into valuable compounds, such as alcohols and carbonyl compounds, has attracted much attention because these systems can operate under mild conditions without toxic oxidants or flammable solvents. The key requirements to achieve such oxidation reactions are (1) highly reactive species on an electrocatalyst for the activation of C–H bonds and (2) efficient transportation pathway for water-insoluble hydrocarbons to an electrode surface. We have determined that a gas diffusion electrode (GDE) supporting Ru atom-modified covalent triazine frameworks (Ru-CTF) has an activity for the electrooxidation of gaseous ethylbenzene to acetophenone using an aqueous electrolyte. A high-valency RuO species was formed in Ru-CTF as an effective active site for O-atom insertion into stable C–H bonds. Furthermore, Ru-CTF showed excellent stability during four consecutive cycles with the replacement of the electrolyte every 12 h, although the reactive RuO species is generated. As for the transportation pathway for substrates, the amount of acetophenone generated from gaseous ethylbenzene was much larger than that from ethylbenzene dissolved in an electrolyte. This result indicates that the three-dimensional microstructures in the GDE maximize the transportation of gaseous hydrocarbons and the oxidation reaction occurs at the triple-phase boundary, which enables the use of aqueous electrolytes.

Selective single-atom electrocatalysts: a review with a focus on metal-doped covalent triazine frameworks

“…4g). 58 By contrast, the generated acetophenone was almost negligible when a bare CTF (i.e., without Ru) was used (green points in Fig. 4g).…”

“…This report was the rst demonstration that single-atom electrocatalysts can catalyse electrochemical hydrocarbon oxidation reactions in aqueous electrolytes. 58 Notably, the degradation of the ethylbenzene oxidation activity of the Ru-CTF was negligible even aer 48 h of electrolysis. This stability is much better than that of the corresponding Ru-based organometallics.…”

“…4f). 58 When a potential of 1.5 V vs. RHE was applied to the GDE electrode, acetophenone was conrmed to be selectively generated as the product of ethylbenzene oxidation without other detectable products. The concentration of generated acetophenone reached 8.3 mmol aer 12 h of electrolysis (blue points in Fig.…”

“…This stability is much better than that of the corresponding Ru-based organometallics. 58 Selective CO 2 reduction reaction vs. hydrogen evolution Excessive emission of CO 2 from the use of fossil fuels is becoming a serious issue for the sustainable development of our society. Thus, developing technologies that use CO 2 as an alternative carbon feedstock and transform it into valuable chemicals, thereby creating a closed carbon cycle, is important.…”

Development of Robust Electrocatalysts Comprising Single-atom Sites with Designed Coordination Environments

“…In addition to an O 2 -tolerant HOR, the Pt-CTFs also show various unique electrocatalytic selectivities. 35,[39][40][41][42][43][44] For example, although the ORR activity of Pt-CTF is not as promising as its HOR activity, it exhibits excellent methanol tolerance during the ORR, which is an attractive property for anode catalysts used in direct methanol fuel cells. 35 Pt-CTF was also inactive toward the nitrate reduction reaction, which is facilitated by bulk Pt metal.…”