Catalytic reduction systems of 2-furancarboxylic acid (FCA) and 2,5-furandicarboxylic acid (FDCA) with H₂ without reduction of the carboxyl groups are reviewed. FCA and FDCA are produced from furfural and 5-hydroxymethylfurfural which are important platform chemicals in biomass conversions. Furan ring hydrogenation to tetrahydrofuran-2-carboxylic acid (THFCA) and tetrahydrofuran-2,5-dicarboxylic acid (THFDCA) easily proceeds over Pd catalysts. Hydrogenolysis of one C–O bond in the furan ring produces 5-hydroxyvaleric acid (5-HVA) and 2-hydroxyadipic acid. 2-Hydroxyvaleric acid is not produced in the reported systems. 5-HVA can be produced as the lactone form (δ-valerolactone; DVL) or as the esters depending on the solvent. These reactions proceed over Pt catalysts with good yields (~ 70%) at optimized conditions. Hydrogenolysis of two C–O bonds in the furan ring produces valeric acid and adipic acid, the latter of which is a very important chemical in industry and its production from biomass is of high importance. Adipic acid from FDCA can be produced directly over Pt-MoO _x catalyst, indirectly via hydrogenation and hydrodeoxygenation as one-pot reaction using the combination of Pt and acid catalysts such as Pt/niobium oxide, or indirectly via two-step reaction composed of hydrogenation catalyzed by Pd and hydrodeoxygenation catalyzed by iodide ion in acidic conditions. Only the two-step method can give good yield of adipic acid at present.

Capturing CO₂ from the atmosphere and converting it into fuels are an efficient strategy to stop the deteriorating greenhouse effect and alleviate the energy crisis. Among various CO₂ conversion approaches, electrocatalytic CO₂ reduction reaction (CO₂RR) has received extensive attention because of its mild operating conditions. However, the high onset potential, low selectivity toward multi-carbon products and poor cruising ability of CO₂RR impede its development. To regulate product distribution, previous studies performed electrocatalyst modification using several universal methods, including composition manipulation, morphology control, surface modification, and defect engineering. Recent studies have revealed that the cathode and electrolytes influence the selectivity of CO₂RR via pH changes and ionic effects, or by directly participating in the reduction pathway as cocatalysts. This review summarizes the state-of-the-art optimization strategies to efficiently enhance CO₂RR selectivity from two main aspects, namely the cathode electrocatalyst and the electrolyte.

A correction to this paper has been published: https://doi.org/10.1007/s12209-021-00286-8

As an energy-intensive industry, the chlor-alkali process has caused numerous environmental issues due to heavy electricity consumption and pollution. Chlor-alkali industry has been upgraded from mercury, diaphragm electrolytic cell, to ion exchange membrane (IEM) electrolytic cells. However, several challenges, such as the selectivity of the anodic reaction, sluggish kinetics of alkaline hydrogen evolution, degradation of membranes, the reasonable design of electrolytic cell structure, remain to be addressed. For these reasons, this paper mainly reviews the research progress of the chlor-alkali industry from materials to devices, including hydrogen evolution anode, chlorine evolution cathode, IEM, and electrolytic cell system. Finally, the research directions and prospects in the chlor-alkali industry are proposed for its further improvement.

A growing family of two-dimensional (2D) transition metal carbides or nitrides, known as MXenes, have received increasing attention because of their unique properties, such as metallic conductivity and good hydrophilicity. The studies on MXenes have been widely pursued, given the composition diversity of the parent MAX phases. This review focuses on MXene films, an important form of MXene-based materials for practical applications. We summarized the synthesis methods of MXenes, focusing on emerging synthesis strategies and reaction mechanisms. The advanced assembly technologies of MXene films, including vacuum-assisted filtration, spin-coating methods, and several other approaches, were then highlighted. Finally, recent progress in the applications of MXene films in electrochemical energy storage, membrane separation, electromagnetic shielding fields, and burgeoning areas, as well as the correlation between compositions, architecture, and performance, was discussed.

Potassium-ion batteries (KIBs) are considered the next powerful potential generation energy storage system because of substantial potassium resource availability and similar characteristics with lithium. Unfortunately, the actual application of KIBs is inferior to that of lithium-ion batteries (LIBs), in which the finite energy density, ordinary circular life, and underdeveloped fabrication technique dominate the key constraints. Various works have recently been directed to growing novel anode electrodes with superior electrochemical capability. Noticeably, metals/metal oxides materials (e.g., Sb, Sn, Zn, SnO₂, and MoO₂) have been widely investigated as KIBs anodes because of high theoretical capacity, suggesting outstanding promise for high-energy KIBs. In this review, the latest research of metals/metal oxides electrodes for potassium storage is summarized. The major strategies to control the electrochemical property of metals/metal oxides electrodes are discussed. Finally, the future investigation foreground for these anode electrodes has been proposed.

The metal oxide/nitrogen-doped carbon (NC) compounds zirconium oxide/NC (ZrO₂/NC) and cerium oxide/NC (CeO₂/NC) were synthesized via the pyrolysis of polyaniline on the metal oxide surface. The characterization of the ZrO₂/NC and CeO₂/NC catalysts showed more active CO₂ reduction reaction activity than that of NC catalyst without metal oxide. Gas chromatography analysis revealed that CO and H₂ were the primary products, and no liquid-phase products were detected via proton nuclear magnetic resonance spectroscopy or high-performance liquid chromatography. The maximum Faraday efficiency of ZrO₂/NC reached 90% at − 0.73 V (vs. RHE), with the current density of CO at 5.5 mA/cm²; this Faraday efficiency value was higher than that of NC (41%), with the current density of CO at 3.1 mA/cm². The interaction between the metal oxide and carbon allowed the efficient formation of defect sites, especially imine-type nitrogen, strengthening the adsorption of the key reaction intermediate CO₂ ^•− and thus promoting the CO₂ reduction reaction.