Due to global warming concerns, major efforts have been devoted to reducing CO₂ emission by switching from the use of coal to other clean fuels, such as natural gas. However, since coal is the most abundant hydrocarbon resource, it would be helpful to develop a non-traditional approach for the utilization of coal that substantially reduces its climate impacts, e.g., electro-oxidation of coal.

Electro-oxidation of coal has been studied for many years. The basic concept provides for the production of gaseous pure hydrogen fuel (H₂), along with a separate stream of CO₂, and these products can be achieved at relatively mild reaction conditions as compared to conventional coal gasification. However, due to the formation of a diffusive barrier film at the coal surface during the oxidation reaction, sufficiently high kinetic rates leading to an acceptable level of conversion have not been achieved at atmospheric pressure. In addition, to obtain desired reaction rate and electrode stability, noble metal materials have to be used in this process, resulting in higher cost and a higher barrier for potential commercialization. To solve these problems, a modified electro-oxidation of coal concept has been developed, by combining pyrolysis and photo-electro-catalysis technology.

As a widely used photo catalyst, black TiO₂ nanotube arrays (bTNA) have been intensively studied as the anode material in the area of photo-assisted water electrolysis. However, in nontransparent systems, use of this process is still a challenge. In this modified process, coal can be oxidized by bTNA with the aid of sunlight, with iron cations serving as the shuttle catalyst. Along with the development of this concept, a series of parameters (e.g., the reaction conditions and methods for electrode preparation) were also examined to facilitate higher kinetic rates, higher coal conversions and overall higher energy efficiency.