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.
Highlights
Methane is a major ingredient in biogas, natural gas, coal-bed gas, shale gas, and gas hydrates
The conduction band minimum (CBM) does not directly affect the PEC oxidation reaction in n-type semiconductor materials, but it is desirable that the CBM of the semiconductor electrode should have a more negative energy level than 0 V vs. RHE (E◦ H+/H2 )
The PEC methane oxidation system, in which abundant methane can be transformed into value-added products using solar light, is considered as an ideal solution to replace the present oil-based chemical industry
Summary
Methane is a major ingredient in biogas, natural gas, coal-bed gas, shale gas, and gas hydrates. The chemical transformation of methane generally requires harsh reaction conditions. Most commercial chemical processes from methane are based on an indirect pathway, which first involves the production of syngas (CO + H2 ), followed by subsequent chemical. Most commercial chemical processes from methane are based on an indirect pathway, which first involves the production of syngas (CO + H2), followed by subsequent processes to synthesize various platform chemicals through C1 chemistry. To utilize small natural gas resources, there for the direct transformation of methane into value-added chemicals. The oxidation energy is provided by increasing the temperature of the system. C-Hthe bond methane is higher than that ofthat partially oxidized chemicals, resulting in down. The dissociation energy of ing in the production of the fully oxidized product (CO2).
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