Here, we have developed porous nanostructured Zn electrocatalysts for CO2 reduction reaction (CO2RR), fabricated by reducing electrodeposited ZnO (RE-Zn) to activate the CO2RR electrocatalytic performance. We discovered that the electrochemical activation environment using CO2-bubbled electrolyte during reducing ZnO in a pretreatment step is important for highly selective CO production over H2 production, while using Ar gas bubbling instead can lead to less CO product of the Zn-based catalyst in CO2RR later. The RE-Zn activated in CO2-bubbled electrolyte condition achieves a Faradaic efficiency of CO production (FECO) of 78.5%, which is about 10% higher than that of RE-Zn activated in Ar-bubbled electrolyte. The partial current density of CO product had more 10-fold increase with RE-Zn electrodes than that of bulk Zn foil at −0.95 V vs RHE in KHCO3. In addition, a very high FECO of 95.3% can be reached using the CO2-pretreated catalyst in KCl electrolyte. The higher amount of oxidized zinc states has been found in the high performing Zn electrode surface by high-resolution X-ray photoelectron spectroscopy studies, which suggest that oxidized zinc states induce the active sites for electrochemical CO2RR. Additionally, in pre- and post-CO2RR performance tests, the carbon deposition is also significantly suppressed on RE-Zn surfaces having a higher ratio of oxidized Zn state.

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.

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.

Photocatalytic materials for photocatalysis is recently proposed as a promising strategy to address environmental remediation. Metal-free graphitic carbon nitride (g-C 3 N 4 ), is an emerging photocatalyst in sulfate radical based advanced oxidation processes. The solar-driven electronic excitations in g-C 3 N 4 are capable of peroxo (O-O) bond dissociation in peroxymonosulfate/peroxydisulfate (PMS/PDS) and oxidants to generate reactive free radicals, namely SO 4•− and OH • in addition to O 2 •− radical. The synergistic mechanism of g-C 3 N 4 mediated PMS/ PDS photocatalytic activation, could ensure the generation of OH • radicals to overcome the low reductive potential of g-C 3 N 4 and fastens the degradation reaction rate. This article reviews recent work on heterojunction formation (type-II heterojunction and direct Z-scheme) to achieve the bandgap for extended visible light absorption and improved charge carrier separation for efficient photocatalytic efficiency. Focus is placed on the fundamental mechanistic routes followed for PMS/PDS photocatalytic activation over g-C 3 N 4 -based photocatalysts. A particular emphasis is given to the factors influencing the PMS/PDS photocatalytic activation mechanism and the contribution of SO 4 •− and OH • radicals that are not thoroughly investigated and require further studies. Concluding perspectives on the challenges and opportunities to design highly efficient persulfateactivated g-C 3 N 4 based photocatalysts toward environmental remediation are also intensively highlighted.

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Metal–oxide interfaces provide a new opportunity to improve catalytic activity based on electronic and chemical interactions at the interface. Constructing a high density of interfaces is essential in maximizing synergistic interactions. Here, we demonstrate that Cu–ceria interfaces made by sintering nanocrystals facilitate C–C coupling reactions in electrochemical reduction of CO2. The Cu/ceria catalyst enhances the selectivity of ethylene and ethanol production with the suppression of H2 evolution in comparison with Cu catalysts. The intrinsic activity for ethylene production is enhanced by decreasing the atomic ratio of Cu/Ce, revealing the Cu atoms near ceria are an active site for C–C coupling reactions. The ceria is proposed to weaken the hydrogen binding energy of adjacent Cu sites and stabilize an *OCCO intermediate via an additional chemical interaction with an oxygen atom of the *OCCO. This work offers new insights into the role of the metal–oxide interface in the electrochemical reduction of CO2 to high-value chemicals.

Organic–inorganic metal halide perovskites (HPs) have emerged as new frontier materials for optoelectronic and energy applications. In addition to various well‐known applications, such as solar cells, light‐emitting diodes, photodetectors, and resistive switching memories, HPs can be utilized as efficient photocatalysts for numerous electrochemical reactions, including carbon dioxide (CO2) reduction reactions, hydrogen evolution reaction, photosynthesis, and wastewater treatment. However, the use of HPs toward photo‐driven catalysis remains a tremendous challenge owing to their poor stability in polar solvents. Nevertheless, huge progress has been made to counter this critical issue for improving the performance of HPs as efficient photocatalysts in a wide range of applications. In this review, we first introduce the structures and properties of HPs. Next, we highlight the recent approaches on the fabrication of HPs, including thin films and nanostructures. Strategies for implementing HPs in catalysis systems and their working mechanisms are thoroughly summarized and discussed. Lastly, the current challenges and prospects of the application of HPs toward photocatalytic reactions are fully addressed. © 2020 Society of Chemical Industry