Photocatalytic Hydrogen and Oxygen Evolution Performed by a Long-Afterglow Material.

A micron-sized long-afterglow material, Sr2MgSi2O7:Eu,Ce, was utilized to conduct the hydrogen evolution reaction and oxygen evolution reaction, two half-reactions of water splitting, in the presence of sacrificial agents under both light and dark conditions for the first time. The as-synthesized Sr2MgSi2O7:Eu,Ce exhibited higher photocatalytic activity compared to that of the referenced Sr2MgSi2O7:Eu and Sr2MgSi2O7:Ce samples. Herein, in addition to benefiting from the long photogenerated carrier lifetime of long-afterglow materials, the higher photocatalytic activity was attributed to the conjugated electronic structure between Eu and Ce ions. This structure facilitates charge and energy transfer between them, leading to an enhanced photocatalytic efficiency. This research provides a new strategy for designing efficient long-afterglow material photocatalysts through the construction of conjugated electronic structures.

Honeycomb Carbon Nanofibers: A Superhydrophilic O2 -Entrapping Electrocatalyst Enables Ultrahigh Mass Activity for the Two-Electron Oxygen Reduction Reaction.

Electrocatalytic two-electron oxygen reduction has emerged as a promising alternative to the energy- and waste-intensive anthraquinone process for distributed H2 O2 production. This process, however, suffers from strong competition from the four-electron pathway leading to low H2 O2 selectivity. Herein, we report using a superhydrophilic O2 -entrapping electrocatalyst to enable superb two-electron oxygen reduction electrocatalysis. The honeycomb carbon nanofibers (HCNFs) are robust and capable of achieving a high H2 O2 selectivity of 97.3 %, much higher than that of its solid carbon nanofiber counterpart. Impressively, this catalyst achieves an ultrahigh mass activity of up to 220 A g-1 , surpassing all other catalysts for two-electron oxygen reduction reaction. The superhydrophilic porous carbon skeleton with rich oxygenated functional groups facilitates efficient electron transfer and better wetting of the catalyst by the electrolyte, and the interconnected cavities allow for more effective entrapping of the gas bubbles. The catalytic mechanism is further revealed by in situ Raman analysis and density functional theory calculations.

Highly Selective Electrochemical Reduction of CO2 to Alcohols on an FeP Nanoarray.

Electrochemical reduction of CO2 into various chemicals and fuels provides an attractive pathway for environmental and energy sustainability. It is now shown that a FeP nanoarray on Ti mesh (FeP NA/TM) acts as an efficient 3D catalyst electrode for the CO2 reduction reaction to convert CO2 into alcohols with high selectivity. In 0.5 m KHCO3 , such FeP NA/TM is capable of achieving a high Faradaic efficiency (FE CH 3 OH ) up to 80.2 %, with a total FE CH 3 OH + C 2 H 5 OH of 94.3 % at -0.20 V vs. reversible hydrogen electrode. Density functional theory calculations reveal that the FeP(211) surface significantly promotes the adsorption and reduction of CO2 toward CH3 OH owing to the synergistic effect of two adjacent Fe atoms, and the potential-determining step is the hydrogenation process of *CO.

Recent Advances in the Development of Water Oxidation Electrocatalysts at Mild pH.

Developing anodic oxygen evolution reaction (OER) electrocatalysts with high catalytic activities is of great importance for effective water splitting. Compared with the water-oxidation electrocatalysts that are commonly utilized in alkaline conditions, the ones operating efficiently under neutral or near neutral conditions are more environmentally friendly with less corrosion issues. This review starts with a brief introduction of OER, the importance of OER in mild-pH media, as well as the fundamentals and performance parameters of OER electrocatalysts. Then, recent progress of the rational design of electrocatalysts for OER in mild-pH conditions is discussed. The chemical structures or components, synthetic approaches, and catalytic performances of the OER catalysts will be reviewed. Some interesting insights into the catalytic mechanism are also included and discussed. It concludes with a brief outlook on the possible remaining challenges and future trends of neutral or near-neutral OER electrocatalysts. It hopefully provides the readers with a distinct perspective of the history, present, and future of OER electrocatalysts at mild conditions.

A Biomass-Derived Carbon-Based Electrocatalyst for Efficient N2 Fixation to NH3 under Ambient Conditions.

Currently, NH3 production primarily depends on the Haber-Bosch process, which operates at elevated temperatures and pressures and leads to serious CO2 emissions. Electrocatalytic N2 reduction offers an environmentally benign approach for the sustainable synthesis of NH3 under ambient conditions. This work reports the development of biomass-derived amorphous oxygen-doped carbon nanosheet (O-CN) using tannin as the precursor. As a metal-free electrocatalyst for N2 -to-NH3 conversion, such O-CN shows high catalytic performances, achieving a large NH3 yield of 20.15 µg h-1 mg-1 cat. and a high Faradic efficiency of 4.97 % at -0.6 V vs. reversible hydrogen electrode (RHE) in 0.1 m HCl at ambient conditions. Remarkably, it also exhibits high electrochemical selectivity and durability.

Round-the-Clock Photocatalytic Hydrogen Production with High Efficiency by a Long-Afterglow Material.

Long afterglow materials can store and release light energy after illumination. A brick-like, micrometer-sized Sr2 MgSi2 O7 :Eu2+ ,Dy3+ long-afterglow material is used for hydrogen production by the photocatalytic reforming of methanol under round-the-clock conditions for the first time, achieving a solar-to-hydrogen (STH) conversion efficiency of 5.18 %. This material is one of the most efficient photocatalysts and provides the possibility of practical use on a large scale. Its remarkable photocatalytic activity is attributed to its unique carrier migration path and large number of lattice defects. These findings expand the application scope of long afterglow materials and provide a new strategy to design efficient photocatalysts by constructing trap levels that can prolong carrier lifetimes.

Greatly Improving Electrochemical N2 Reduction over TiO2 Nanoparticles by Iron Doping.

Titanium-based catalysts are needed to achieve electrocatalytic N2 reduction to NH3 with a large NH3 yield and a high Faradaic efficiency (FE). One of the cheapest and most abundant metals on earth, iron, is an effective dopant for greatly improving the nitrogen reduction reaction (NRR) performance of TiO2 nanoparticles in ambient N2 -to-NH3 conversion. In 0.5 m LiClO4 , Fe-doped TiO2 catalyst attains a high FE of 25.6 % and a large NH3 yield of 25.47 µg h-1 mgcat -1 at -0.40 V versus a reversible hydrogen electrode. This performance compares favorably to those of all previously reported titanium- and iron-based NRR electrocatalysts in aqueous media. The catalytic mechanism is further probed with theoretical calculations.

Mn3 O4 Nanocube: An Efficient Electrocatalyst Toward Artificial N2 Fixation to NH3.

Traditionally, ammonia (NH3 ) is synthesized via the Haber-Bosch process, which is not only commanded by harsh conditions but causes serious environmental pollution. Electrochemical reduction is recognized as a mild and environmentally benign alternative approach for NH3 synthesis, but an efficient electrocatalyst is a prerequisite for NH3 production. In this communication, the first experimental demonstration that Mn3 O4 nanocubes can be used as an efficient non-noble-metal electrocatalyst for N2 reduction reaction (NRR) at ambient conditions is reported. In 0.1 m Na2 SO4 aqueous solution, the catalyst delivers excellent NRR activity with an NH3 yield of 11.6 µg h-1 mg-1 cat. and Faradaic efficiency of 3.0% at -0.8 V versus reversible hydrogen electrode. Notably, this catalyst also possesses satisfactory durability during the electrolysis and recycling test.

Nanostructured Bromide-Derived Ag Film: An Efficient Electrocatalyst for N2 Reduction to NH3 under Ambient Conditions.

Electrochemical reduction has been regarded as a sustainable strategy to tackle energy-intensive operations by the Haber-Bosch process achieving catalytic conversion of N2 to NH3 under mild conditions. However, the challenge of N2 electroconversion emphasizes the requirement of efficient electrocatalysts. In this paper, we report the development of porous bromide-derived Ag film (BD-Ag/AF) as an efficient electrocatalyst for N2 reduction reaction. During electrochemical test, Br- anions are released and adsorbed onto the surfaces of the electrode, suppressing hydrogen evolution reaction. Such BD-Ag/AF shows a high Faradaic efficiency of 7.36% at -0.6 V vs reversible hydrogen electrode in 0.1 M Na2SO4, which is higher than that (0.38%) of porous Ag film without Br- anions. Moreover, it exhibits excellent long-term electrochemical durability.

IR-Driven Photocatalytic Water Splitting with WO2-NaxWO3 Hybrid Conductor Material.

An IR-driven photocatalytic water splitting system based on WO2-NaxWO3 (x > 0.25) hybrid conductor materials was established for the first time; this system can be directly applied in seawater. The WO2-NaxWO3 (x > 0.25) hybrid conductor material was readily prepared by a high-temperature reduction process of semiconductor NaxWO3 (x < 0.25) nanowire bundles. A novel ladder-type carrier transfer process is suggested for the established IR-driven photocatalytic water splitting system.

Effect of bromide on molecular transformation of dissolved effluent organic matter during ozonation, UV/H2O2, UV/persulfate, and UV/chlorine treatments.

Ozonation and ultraviolet-based advanced oxidation processes (UV-AOPs) play important roles in advanced treatment of municipal wastewater for water reuse. Bromide is widely present in wastewater at different concentration levels (ranging from µg/L to mg/L). However, the effect of bromide on molecular transformation of dissolved effluent organic matter (dEfOM) in real wastewater during ozonation and UV-AOPs treatments still remains unclear. Herein, Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) was utilized to characterize the overall molecular transformation of dEfOM and the formation of unknown halogenated byproducts (X-BPs) in ozonation, UV/H2O2, UV/persulfate (UV/PS), and UV/chlorine (UV/Cl) processes in the presence of additional bromide. Compared with the same oxidation processes without additional bromide, the degree of dEfOM oxygenation had some extent decrement with the effect of bromide. A slightly increment of the number of unknown brominated byproducts (Br-BPs) was observed during ozonation, UV/H2O2, and UV/PS treatments in the presence of additional bromide, and the largest increment of these compounds was found in UV/Cl process. A total of 82 chlorinated byproducts (Cl-BPs) and 183 Br-BPs were detected in all oxidation processes with the effect of bromide, and the number of Br-BPs was significantly higher than that of Cl-BPs. Based on mass difference analysis, 69 pairs of possible precursors/Br-BPs were identified. In addition, the additional bromide did not remarkably increase the concentrations of trihalomethanes (THMs) and haloacetic acids (HAAs) in ozonation, UV/H2O2, and UV/PS treatments, while the production of THMs and HAAs significantly decreased by 68.06% and 54.55%, respectively, during UV/Cl treatment. The calculated cytotoxicity increased to some extent for each treatment, especially for UV/Cl treatment, and the compound with largest contribution to cytotoxicity was monobromoacetic acid. This study provides new insights into the formation and transformation of X-BPs during advanced treatment of real wastewater with the effect of bromide.

Ni2P nanosheet array for high-efficiency electrohydrogenation of nitrite to ammonia at ambient conditions.

Ammonia (NH3) plays an important role in agriculture and industry. The industry-scale production mainly depends on the Haber-Bosch process suffering from issues of environment pollution and energy consumption. Electrochemical reduction can degrade nitrite (NO2-) pollutants in the environment and convert it into more valuable NH3. Here, Ni2P nanosheet array on nickel foam is proposed as a 3D electrocatalyst for high-efficiency electrohydrogenation of NO2- to NH3 under ambient reaction conditions. When tested in 0.1 M phosphate buffer saline with 200 ppm NO2-, such Ni2P/NF is able to obtain a large NH3 yield rate of 2692.2 ± 92.1 µg h-1 cm-2 (3282.9 ± 112.3 µg h-1 mgcat.-1), a high Faradic efficiency of 90.2 ± 3.0%, and selectivity of 87.0 ± 1.7% at -0.3 V versus a reversible hydrogen electrode. After 10 h of electrocatalytic reduction, the conversion rate of NO2- achieves near 100%. The catalytic mechanism is further investigated by density functional theory calculations.

Green preparation of porous hierarchical TiO2(B)/anatase phase junction for effective photocatalytic degradation of antibiotics.

In this study, porous hierarchical bronze/anatase phase junction TiO2 assembled by ultrathin two-dimensional nanosheets was prepared by a novel, green and simple deep eutectic solvent-regulated strategy. Due to its structural features, the TiO2 sample exhibited enhanced photocatalytic activities for multiple kinds of antibiotics, including ofloxacin, ciprofloxacin and chloramphenicol.

High-efficiency nitrate electroreduction to ammonia on electrodeposited cobalt-phosphorus alloy film.

Electrocatalytic eight-electron nitrate (NO3-) reduction is a sustainable strategy to degrade NO3- and convert it into high value-added ammonia (NH3) but needs efficient catalysts with high activity and selectivity. Our study shows the use of Ti plate supported cobalt-phosphorus alloy film (Co-P/TP) as a highly active and selective electrocatalyst for ambient NO3--to-NH3 conversion. In 0.2 M Na2SO4 with 200 ppm NO3-, Co-P/TP offers an NH3 yield rate of 416.0 ± 7.2 µg h-1 cm-2 and a high faradaic efficiency of 93.6 ± 3.3% at -0.6 V and -0.3 V vs. reversible hydrogen electrode, respectively, with good durability. Noticeably, a conversion rate of 86.9% is achieved after 10 h bulk electrolysis.

Ti2O3 Nanoparticles with Ti3+ Sites toward Efficient NH3 Electrosynthesis under Ambient Conditions.

Electrocatalytic nitrogen reduction reaction (NRR) enabled by introducing Ti3+ defect sites into TiO2 through a doping strategy has recently attracted widespread attention. However, the amount of Ti3+ ions is limited due to the low concentration of dopants. Herein, we propose Ti2O3 nanoparticles as a pure Ti3+ system that performs efficiently toward NH3 electrosynthesis under ambient conditions. This work has suggested that Ti3+ ions, as the main catalytically active sites, significantly increase the NRR activity. In an acidic electrolyte, Ti2O3 achieves extraordinary performance with a high NH3 yield and a Faradaic efficiency of 26.01 µg h-1 mg-1 cat. and 9.16%, respectively, which are superior to most titanium-based NRR catalysts recently reported. Significantly, it also demonstrates a stable NH3 yield in five consecutive cycles. Theoretical calculations uncovered that the enhanced electrocatalytic activity of Ti2O3 originated from Ti3+ active sites and significantly lowered the overpotential of the potential-determining step.

Enhanced Electrochemical H2O2 Production via Two-Electron Oxygen Reduction Enabled by Surface-Derived Amorphous Oxygen-Deficient TiO2-x.

The electrochemical oxygen reduction reaction (ORR) is regarded as an attractive alternative to the anthraquinone process for sustainable and on-site hydrogen peroxide (H2O2) production. It is however hindered by low selectivity due to strong competition from the four-electron ORR and needs efficient catalysts to drive the 2e- ORR. Here, an acid oxidation strategy is proposed as an effective strategy to boost the 2e- ORR activity of metallic TiC via in-site generation of a surface amorphous oxygen-deficient TiO2-x layer. The resulting a-TiO2-x/TiC exhibits a low overpotential and high H2O2 selectivity (94.1% at 0.5 V vs reversible hydrogen electrode (RHE)), and it also demonstrates robust stability with a remarkable productivity of 7.19 mol gcat.-1 h-1 at 0.30 V vs RHE. The electrocatalytic mechanism of a-TiO2-x/TiC is further revealed by density functional theory calculations.

Grey Rutile TiO2 with Long-Term Photocatalytic Activity Synthesized Via Two-Step Calcination.

Colored titanium oxides are usually unstable in the atmosphere. Herein, a gray rutile titanium dioxide is synthesized by two-step calcination successively in a high-temperature reduction atmosphere and in a lower-temperature air atmosphere. The as-synthesized gray rutile TiO2 exhibits higher photocatalytic activity than that of white rutile TiO2 and shows high chemical stability. This is attributed to interior oxygen vacancies, which can improve the separation and transmission efficiency of the photogenerated carriers. Most notably, a formed surface passivation layer will protect the interior oxygen vacancies and provide long-term photocatalytic activity.

Cu3P nanoparticle-reduced graphene oxide hybrid: an efficient electrocatalyst to realize N2-to-NH3 conversion under ambient conditions.

Industrial NH3 synthesis mainly relies on the Haber-Bosch process operated under harsh conditions. Ambient electrochemical N2 reduction offers an eco-friendly and sustainable pathway for NH3 synthesis, but its implementation depends on efficient electrocatalysts. Here, we report that a Cu3P nanoparticle-reduced graphene oxide (Cu3P-rGO) hybrid serves as an efficient electrocatalyst toward NH3 synthesis. Tested in 0.1 M HCl, Cu3P-rGO exhibits a large NH3 yield of 26.38 µg h-1 mgcat.-1 and a high faradaic efficiency of 10.11% at -0.45 V vs. the reversible hydrogen electrode, with high electrochemical stability. Theoretical calculations reveal that Cu3P can efficiently catalyze NH3 synthesis.

Photocatalytic Overall Water Splitting by SrTiO3 with Surface Oxygen Vacancies.

Strontium Titanate has a typical perovskite structure with advantages of low cost and photochemical stability. However, the wide bandgap and rapid recombination of electrons and holes limited its application in photocatalysis. In this work, a SrTiO3 material with surface oxygen vacancies was synthesized via carbon reduction under a high temperature. It was successfully applied for photocatalytic overall water splitting to produce clean hydrogen energy under visible light irradiation without any sacrificial reagent for the first time. The photocatalytic overall water splitting ability of the as-prepared SrTiO3-C950 is attributed to the surface oxygen vacancies that can make suitable energy levels for visible light response, improving the separation and transfer efficiency of photogenerated carriers.

Enhanced electrocatalytic N2-to-NH3 fixation by ZrS2 nanofibers with a sulfur vacancy.

Industrially, large-scale NH3 production is achieved by the Haber-Bosch process, which operates under harsh reaction conditions with abundant energy consumption and CO2 emission. Electrochemical N2 reduction is an eco-friendly and energy-saving method for artificial N2 to NH3 fixation under ambient reaction conditions. Herein, we demonstrate that ZrS2 nanofibers with a sulfur vacancy (ZrS2 NF-Vs) behave as an efficient electrocatalyst for ambient N2 reduction to NH3 with excellent selectivity. In 0.1 M HCl, this ZrS2 NF-Vs catalyst attains a large NH3 yield of 30.72 µg h-1 mgcat.-1 and a high faradaic efficiency of 10.33% at -0.35 V and -0.30 V vs. reversible hydrogen electrode, respectively. It also shows high electrochemical and structural stability. The density functional theory calculations reveal that the introduction of Vs facilitates the adsorption and activation of N2 molecules.