Titanium dioxide (TiO₂) has attracted increasing attention as a candidate for the photocatalytic reduction of carbon dioxide (CO₂) to convert anthropogenic CO₂ gas into fuels combined with storage of intermittent and renewable solar energy in forms of chemical bonds for closing the carbon cycle. However, pristine TiO₂ possesses a large band gap (3.2 eV), fast recombination of electrons and holes, and low selectivity for the photoreduction of CO₂. Recently, considerable progress has been made in the improvement of the performance of TiO₂ photocatalysts for CO₂ reduction. In this review, we first discuss the fundamentals of and challenges in CO₂ photoreduction on TiO₂-based catalysts. Next, the recently emerging progress and advances in TiO₂ nanostructured and hybrid materials for overcoming the mentioned obstacles to achieve high light-harvesting capability, improved adsorption and activation of CO₂, excellent photocatalytic activity, the ability to impede the recombination of electrons-holes pairs, and efficient suppression of hydrogen evolution are discussed. In addition, approaches and strategies for improvements in TiO₂-based photocatalysts and their working mechanisms are thoroughly summarized and analyzed. Lastly, the current challenges and prospects of CO₂ photocatalytic reactions on TiO₂-based catalysts are also presented.

The conversion of carbon dioxide (CO₂) to valuable fuels and chemicals offers a new pathway for sustainable and clean carbon fixation. Recently, the focus has been on electrochemical CO₂ reduction on heterogeneous electrode catalysts, leading to remarkable achievements in the reaction performance. To date, CO₂ to carbon monoxide (CO) conversion is considered as the most promising candidate reaction for the industrial market, owing to its high efficiency and reasonable technoeconomic feasibility. Moreover, CO has been proposed as a key intermediate species for further reduced hydrocarbons, which can pave the way for various fuel production. This study sets out to describe recent progress on the electrochemical CO₂ reduction to CO in a heterogeneously catalyzed system. The review includes understanding of the catalytic material employed and engineering strategies implemented by adjusting the binding energy of key adsorbates. These material design approaches, such as nanostructuring, alloying, doping, and so forth, have pioneered breakouts in the intrinsic catalytic nature of transition metal elements. Moreover, recent advances in systematic design are summarized, with focus on practical industrial applications. Finally, perspectives on the design of electrocatalyst materials for CO production by electrochemical CO₂ reduction are presented.

Low dimensional transition metal carbide and nitride (MXenes) have been emerging as frontier materials for energy storage and conversion. Ti₃C₂T_x was the first MXenes that discovered and soon become the most widely investigated among the MXenes family. Interestingly, Ti₃C₂T_x exhibits ultrahigh catalytic activity towards the hydrogen evolution reaction. In addition, Ti₃C₂T_x is electronically conductive, and its optical bandgap is tunable in the visible region, making it become one of the most promising candidates for the photocatalytic hydrogen evolution reaction (HER). In this review, we provide comprehensive strategies for the utilization of Ti₃C₂T_x as a catalyst for improving solar-driven HER, including surface functional groups engineering, structural modification, and cocatalyst coupling. In addition, the reaming obstacle for using these materials in a practical system is evaluated. Finally, the direction for the future development of these materials featuring high photocatalytic activity toward HER is discussed.