Photoelectrochemical Conversion of Methane into Value-Added Products

Abstract

Methane has been reported to be directly converted into value-added products through various methods. Among them, photoelectrochemical (PEC) methane conversion is considered an eco-friendly method because it utilizes solar light and is able to control the selectivity to different products by means of application of an external bias. Recently, some PEC methane conversion systems have been reported, but their performance efficiencies are relatively lower than those of other existing thermal, photocatalytic, and electrochemical systems. The detailed mechanism of methane activation is not clear at this stage. In this review, various catalytic materials and their roles in the reaction pathways are summarized and discussed. Furthermore, promising semiconductor materials, co-catalysts, and oxidants have also been proposed. Finally, direct and indirect pathways in the design of the PEC methane conversion system have been discussed.

Photoelectrocatalytic conversion of biomethane and biogas to hydrogen over a nanostructured Ti/ TiO 2 semiconductor

“…Activation of methane occurs by photogenerated holes that capture an electron in the methane molecule to form hydrions (H + ) and methyl radicals ( • CH 3 ) on the semiconductor surface. The methyl radicals formed by the oxidation of methane by the holes participate in reactions to form byproducts, and the adsorbed hydrions are then reduced to hydrogen by the photoexcited electrons at the cathode 66,67 …”

Solar Driven Gas Phase Advanced Oxidation Processes for Methane Removal ‐ Challenges and Perspectives

“…Photocatalysis reaction can generate high-energy charge carriers in the process, which can pre-activate CH4 and substantially reduce the activation energy [18] . This pre-activation process enables thermodynamically unfavorable reactions at room temperature, and overcomes traditional thermodynamic barriers (Figure 4) [16] .…”

“…[18] This pre-activation process enables thermodynamically unfavorable reactions at room temperature, and overcomes traditional thermodynamic barriers (Figure 4). [16] Compared with thermal catalysis, photocatalytic reactions can theoretically avoid harsh reaction conditions.…”

“…Figure 4. Schematic energy diagram of methane oxidation with a photocatalyst.Reproduced from ref [16]. with permission from Catalysts, copyright 2021.…”

Understanding (photo)electrocatalysis for the conversion of methane to valuable chemicals through partial oxidation processes

“…88,89 Metal chalcogenide, C 3 N 4 , and metal carbide are also good candidates for visible light PEC CH 4 oxidation because the outstanding photocatalytic activity was already reported for the partial oxidation of CH 4 in slurry-type systems. 90,91 The modication of the bulk and surface properties of semiconducting materials and cocatalysts or the introduction of highly active photocatalysts and electrocatalysts in PEC systems should be helpful to advance the design of the PEC device with high performance under sunlight.…”