Progress in the electrocatalytic oxidation of methane to methanol

Methane as the primary component of natural gas is characterized by abundant reserves, low cost, and high energy density. However, its strong C–H bonds render CH4 activation and functionalization exceedingly challenging, thus, the activation and subsequent functionalization of CH4 is a demanding task. The selective oxidation of methane is therefore often hailed as the “holy grail reaction” in the fields of catalysis and chemical engineering. The activation of the C−H bonds of methane requires harsh conditions, including high temperatures and pressures. Such extreme conditions not only demand substantial energy inputs, but also increase the risk of overoxidation of the desired products resulting in the formation of undesired byproducts and thus reducing the overall selectivity and efficiency of the process. Consequently, the selective conversion of methane into high-value-added chemicals under mild conditions remains a longstanding goal and a formidable challenge. Addressing this challenge is critical to ensure the sustainable and economically viable utilization of methane as a chemical feedstock.Methanol is among the most important liquid-phase products of methane oxidation owing to its high energy density and use as an important chemical feedstock in various industrial applications. Liquid methanol offers significant advantages over gaseous hydrocarbons, especially in terms of transportation and storage, making it an ideal target product for selective methane oxidation. The use of renewable energy sources such as light energy (solar power) and electrical energy to drive the low-temperature catalytic conversion of methane has attracted increasing attention in recent years. In particular, renewable electrical energy shows great promise owing to its abundance and environmental sustainability. Electrical energy can be harnessed to selectively activate the C−H bonds of methane via electrocatalytic processes. This approach overcomes the reaction barriers associated with mild conditions and avoids harsh conditions such as high temperature and pressure, thereby mitigating the problem of over-oxidation. Unlike light energy, which can be intermittent and difficult to control, electrical energy can be supplied continuously, enabling precise control over methane activation and conversion. Additionally, the regeneration and recovery of electrocatalysts are typically more convenient than those of photocatalysts, which further improves the longevity and economic viability of the electrocatalytic process. Electrocatalytic methane oxidation (eCH4OR) has therefore emerged as a promising platform for efficient methane utilization under mild and sustainable conditions.Significant progress has been achieved in the development and application of eCH4OR for methanol production, thus, this review discusses various strategies for eCH4OR across various systems. We systematically introduce recent research that advances our understanding of the mechanisms of methane oxidation using transition metals in liquid-phase systems and examine the optimization of the reaction conditions of such systems. Furthermore, we highlight the role of solid-state electrolyte systems in facilitating efficient electron transfer and improving the overall efficiency of the electrocatalytic process. This comprehensive review of these advances aims to identify the key factors that influence the performance of eCH4OR systems and highlight the innovative approaches developed to overcome existing challenges associated with such systems. Finally, the review highlights the current challenges facing eCH4OR, including issues related to catalyst stability, selectivity, and scalability as well as the need for a deeper understanding of the catalytic reaction mechanisms at the molecular level. Addressing these challenges will facilitate the further development of novel and efficient electrocatalysts and electrocatalytic systems tailored for methanol production via eCH4OR. The insights provided in this review offer valuable research directions that will enable future studies to unlock the full potential of methane as a versatile and sustainable chemical feedstock.