Electrocatalytic Methane Oxidation Greatly Promoted by Chlorine Intermediates

Abstract

Renewable energy-powered methane (CH 4 ) conversion at ambient conditions is an attractive but highly challenging field. Due to the highly inert character of CH 4 , the selective cleavage of its first CÀH bond without over-oxidation is essential for transforming CH 4 into value-added products. In this work, we developed an efficient and selective CH 4 conversion approach at room temperature using intermediate chlorine species (*Cl), which were electrochemically generated and stabilized on mixed cobalt-nickel spinels with different Co/Ni ratios. The lower overpotentials for *Cl formation enabled an effective activation and conversion of CH 4 to CH 3 Cl without over-oxidation to CO 2 , and Ni 3+ at the octahedral sites in the mixed cobalt-nickel spinels allowed to stabilize surface-bound *Cl species. The CoNi 2 O x electrocatalyst exhibited an outstanding yield of CH 3 Cl (364 mmol g À1 h À1 ) and a high CH 3 Cl/CO 2 selectivity of over 400 at room temperature, with demonstrated capability of direct CH 4 conversion under seawater working conditions.

Preferential Adsorption of Ethylene Oxide on Fe and Chlorine on Ni Enabled Scalable Electrosynthesis of Ethylene Chlorohydrin

“…Then, ⋅Cl is formed by losing an electron when the electrolysis is started, which subsequently abstracts an atomic hydrogen from 1 a to generate the radical intermediate I 1a . ⋅Cl‐mediated transformations via abstracting an electron or a ⋅H from the substrates have proved to be very efficient for thermo‐, photo, and electrosynthesis of high‐value products [7, 8, 18] . However, we cannot fully rule out the possibility of an outer sphere ⋅Cl mediated radical process for the formation of I 1a .…”

“…For example, recently Zheng and co‐workers have made an advance on the ⋅Cl‐promoted electrocatalytic CH 4 conversion to CH 3 Cl . [8] Epoxides are important building blocks in organic synthesis, [9] which are predisposed to ring‐opening through single electron oxidation. Thus, we speculate that ⋅Cl generated via Cl − electrooxidation can abstract a ⋅H from EO to form the epoxide radical I , which will quickly experience a C−O bond cleavage to generate the intermediate II due to its large ring strain and inherent electronic bias.…”

Interfacial Micro‐Environment of Electrocatalysis and Its Applications for Organic Electro‐Oxidation Reaction

“…Alkane oxidation reaction is essential to the production of a variety of commodity chemicals including alcohols, [56,[102][103][104][105] alkenes, [55,59,106,107] acetone, [108] halogenated hydrocarbon, [109] and hydrogen. [56] However, such kind of conversion process is bound by the activation of the intrinsically inert C─H bond, of which owns weak polarity and high bond dissociation energy (BDE) (≥100 kcal mol −1 ).…”

“…Copyright 2021, Wiley-VCH. i) (Left) The CH 4 activation pathways, activated by *O (generated from OER) or by *Cl (generated from ClER) and (right) schematic showing the regulation of *Cl intermediate's stability by introducing Ni 3+ into CoNi mixed spinels; Reproduced with permission [109]. Copyright 2021, Wiley-VCH.…”

Current Progress on Methods and Technologies for Catalytic Methane Activation at Low Temperatures

“…The reported catalyst showed outstanding CH 4 to CH 3 Cl activity (364 mmol g −1 h −1 at 2.3 V) and a high CH 3 Cl/CO 2 selectivity in saturated NaCl electrolyte, which was attributed to the catalyst's ability to electrochemically produce *Cl, and Ni 3+ at octahedral sites allowed to stabilize surface‐bound *Cl species better. [ 435 ] Overall, electrocatalytic activation of CH 4 under mild conditions is still early days; an ideal electrocatalyst system should consider the increase of CH 4 conversion and selectivity toward the desired products.…”