Recent advances on bismuth oxyhalides for photocatalytic CO2 reduction.

Photocatalytic conversion of CO2 into fuels such as CO, CH4, and CH3OH, is a promising approach for achieving carbon neutrality. Bismuth oxyhalides (BiOX, where X = Cl, Br, and I) are appropriate photocatalysts for this purpose due to the merits of visible-light-active, efficient charge separation, and easy-to-modify crystal structure and surface properties. For practical applications, multiple strategies have been proposed to develop high-efficiency BiOX-based photocatalysts. This review summarizes the development of different approaches to prepare BiOX-based photocatalysts for efficient CO2 reduction. In the review, the fundamentals of photocatalytic CO2 reduction are introduced. Then, several widely used modification methods for BiOX photocatalysts are systematacially discussed, including heterojunction construction, introducing oxygen vacancies (OVs), Bi-enrichment, heteroatom-doping, and morphology design. Finally, the challenges and prospects in the design of future BiOX-based photocatalysis for efficient CO2 reduction are examined.

Efficient Ammonia Electrosynthesis from Nitrate on Strained Ruthenium Nanoclusters.

The limitations of the Haber-Bosch reaction, particularly high-temperature operation, have ignited new interests in low-temperature ammonia-synthesis scenarios. Ambient N2 electroreduction is a compelling alternative but is impeded by a low ammonia production rate (mostly <10 mmol gcat-1 h-1), a small partial current density (<1 mA cm-2), and a high-selectivity hydrogen-evolving side reaction. Herein, we report that room-temperature nitrate electroreduction catalyzed by strained ruthenium nanoclusters generates ammonia at a higher rate (5.56 mol gcat-1 h-1) than the Haber-Bosch process. The primary contributor to such performance is hydrogen radicals, which are generated by suppressing hydrogen-hydrogen dimerization during water splitting enabled by the tensile lattice strains. The radicals expedite nitrate-to-ammonia conversion by hydrogenating intermediates of the rate-limiting steps at lower kinetic barriers. The strained nanostructures can maintain nearly 100% ammonia-evolving selectivity at >120 mA cm-2 current densities for 100 h due to the robust subsurface Ru-O coordination. These findings highlight the potential of nitrate electroreduction in real-world, low-temperature ammonia synthesis.

Enhanced Phototransformation of Tetracycline at Smectite Clay Surfaces under Simulated Sunlight via a Lewis-Base Catalyzed Alkalization Mechanism.

As an important class of soil minerals and a key constituent of colloidal particles in surface aquifers, smectite clays can strongly retain tetracyclines due to their large surface areas and high cation exchange capacities. However, the research on phototransformation of tetracyclines at smectite clay surfaces is rarely studied. Here, the phototransformation kinetics of tetracycline preadsorbed on two model smectite clays (hectorite and montmorillonite) exchanged with Na+, K+, or Ca2+ suspended in aqueous solution under simulated sunlight was compared with that of tetracycline dissolved in water using batch experiments. Adsorption on clays accelerated tetracycline phototransformation (half-lives shortened by 1.1-5.3 times), with the most significant effects observed for Na+-exchanged clays. Regardless of the presence or absence of clay, the phototransformation of tetracycline was facilitated by increasing pH from 4 to 7. Inhibition or enhancement of photolysis-induced reactive species combined with their measurement using scavenger/probe chemicals indicate that the facilitated production of self-photosensitized singlet oxygen (1O2) was the key factor contributing to the clay-enhanced phototransformation of tetracycline. As evidenced by the red shifts and the increased molar absorptivity in the UV-vis absorption spectra, the complexation of tetracycline with the negatively charged (Lewis base) sites on clay siloxane surfaces led to formation of the alkalized form, which has larger light absorption rate and is more readily to be oxidized compared to tetracycline in aqueous solution at equivalent pH. Our findings indicate a previously unrecognized, important phototransformation mechanism of tetracyclines catalyzed by smectite clays.

Unravelling the carbonate issue through the regulation of mass transport and charge transfer in mild acid.

The electrochemical CO2 reduction reaction (CO2RR) triggered by renewable electricity provides a promising route to produce chemical feedstocks and fuels with low-carbon footprints. The intrinsic challenge for the current CO2RR electrolyzer is the carbonate issue arising from the reaction between hydroxide and CO2. Acid CO2RR electrolyzers, in principle, can effectively solve the carbonate formation, but it remains inevitable practically. In this work, we thoroughly investigated the electrode processes of the CO2RR on the benchmark Ag catalyst in mild acid. The root of the carbonate issue arises from the imbalanced supply-consumption rate of protons-the electron transfer vs. mass transport. Regulating the hydrodynamics substantially reduces the proton diffusion length by 80%, increasing the single-pass carbon utilization efficiency of CO2-to-CO to 44% at -100 mA cm-2. The fundamental difference between mass transport and electron transfer on the spatial and temporal scale still leads to unavoidable carbonate formation. Future work to design intrinsically active catalysts in strong acid or metal-cation-free media is critical to solving the carbonate issue.

Addressing the Carbonate Issue: Electrocatalysts for Acidic CO2 Reduction Reaction.

Electrochemical CO2 reduction reaction (CO2RR) powered by renewable energy provides a promising route to CO2 conversion and utilization. However, the widely used neutral/alkaline electrolyte consumes a large amount of CO2 to produce (bi)carbonate byproducts, leading to significant challenges at the device level, thereby impeding the further deployment of this reaction. Conducting CO2RR in acidic electrolytes offers a promising solution to address the "carbonate issue"; however, it presents inherent difficulties due to the competitive hydrogen evolution reaction, necessitating concerted efforts toward advanced catalyst and electrode designs to achieve high selectivity and activity. This review encompasses recent developments of acidic CO2RR, from mechanism elucidation to catalyst design and device engineering. This review begins by discussing the mechanistic understanding of the reaction pathway, laying the foundation for catalyst design in acidic CO2RR. Subsequently, an in-depth analysis of recent advancements in acidic CO2RR catalysts is provided, highlighting heterogeneous catalysts, surface immobilized molecular catalysts, and catalyst surface enhancement. Furthermore, the progress made in device-level applications is summarized, aiming to develop high-performance acidic CO2RR systems. Finally, the existing challenges and future directions in the design of acidic CO2RR catalysts are outlined, emphasizing the need for improved selectivity, activity, stability, and scalability.

Acid Etching Strategy: Optimizing Bifunctional Activities of Metal/Nitrogen-doped Carbon Catalysts for Efficient Rechargeable Zn-Air Batteries.

Transition metal-embedded heteroatom carbon composites are regarded as an important branch of bifunctional catalysts for rechargeable Zn-air batteries. The inevitable transition metal particles on the carbon skeleton may affect the availability of the metal-heteroatom-carbon catalytic site. Herein, we propose an acid treatment strategy to remove the bare transition metal particles, thus regulating the electrochemical surface area. The OER activities are highly related to the electrochemical surface area for the catalysts with different acid treatment times. In addition, there exists an optimal acid treatment time to achieve the highest ORR and OER activities with the ΔE value of 0.75 V. Given the superior bifunctional activities after acid treatment, we further assemble the rechargeable Zn-air batteries with the optimal catalyst, which achieves a peak power density of 364 mW cm-2 and long cycling life of 500 h at 10 mA cm-2 . This work affords an efficient strategy to enhance the ORR/OER activities and may guide the design of transition metal/heteroatom carbon composites.

Electrochemical generation of hydrogen peroxide from a zinc gallium oxide anode with dual active sites.

Electrochemical water oxidation enables the conversion of H2O to H2O2. It holds distinct advantages to the O2 reduction reaction, which is restricted by the inefficient mass transfer and limited solubility of O2 in aqueous media. Nonetheless, most reported anodes suffer from high overpotentials (usually >1000 mV) and low selectivity. Electrolysis at high overpotentials often causes serious decomposition of peroxides and leads to declined selectivity. Herein, we report a ZnGa2O4 anode with dual active sites to improve the selectivity and resist the decomposition of peroxides. Its faradaic efficiency reaches 82% at 2.3 V versus RHE for H2O2 generation through both direct (via OH-) and indirect (via HCO3-) pathways. The percarbonate is the critical species generated through the conversion of bicarbonate at Ga-Ga dual sites. The peroxy bond is stable on the surface of the ZnGa2O4 anode, significantly improving faradaic efficiency.