Direct conversion of CH₄ and O₂ to value-added chemicals is important for natural gas industries. However, challenges remain due to the difficulty of O₂ activation in forming active oxygen species for CH₄ activation under mild conditions.

Recently, a research group led by Prof. DENG Dehui, Assoc. Prof. CUI xiaoju and YU Liang from the Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences (CAS) realized the electrochemical conversion of CH₄ by O₂ to HCOOH at room temperature. This study was published in Journal of the American Chemical Society.

The researchers developed a high-pressure electro-Fenton strategy to establish a hetero-homogeneous process for electro-catalytic conversion of CH₄ by O₂ at room temperature. They revealed that CH₄ was efficiently activated by ·OH, which was produced via a heterogeneous electroreduction of O₂ to H₂O₂ on the Ag foil cathode, followed by a homogeneous Fe²⁺-facilitated H₂O₂ decomposition.

Besides, the researchers found that the elevated pressure not only improved the productivity of H₂O₂ from O₂ electro-reduction but also boosted the reaction collision probability between CH₄ and active ·OH in-situ generated from Fe²⁺-facilitated decomposition of H₂O₂.

Compared with the traditional electro-catalytic CH₄ conversion process with high overpotential (>0.9 V) and low Faradaic efficiency (< 60%), the high-pressure electro-Fenton process achieved an HCOOH Faradaic efficiency of 81.4% with an ultra-low cathodic overpotential of 0.38 V. The HCOOH productivity was 11.5 mmol h^-1 gFe^-1, which was 220 times that of ambient pressure.

"This work provides a new way for energy-efficient and sustainable conversion of CH₄ by directly using O₂ under mild conditions," said Prof. DENG.

Schematic diagram of CH₄ conversion to HCOOH by the hetero-homogeneous coupling electro-catalytic process (Image by Dehui Deng)