Copper Electrocatalyst Produced by Cu2(OH)2CO3-Mediated In Situ Deposition for Diluted CO2 Reduction to Multicarbon Products.

Pure CO2 is commonly used in most of the current studies for electrochemical CO2 reduction which will need a further cost of gas purification and separation. However, the limited works on diluted CO2 reduction are focused on CO or CH4 production other than C2 products. In this work, copper electrocatalysts were prepared by Cu2(OH)2CO3-mediated in situ deposition for diluted CO2 reduction to multicarbon products. Using in situ Raman spectroscopy, constant amounts of CO and OH* were observed on the catalyst surface, which could effectively suppress the high kinetics of hydrogen evolution and promote C-C coupling, especially under the condition of diluted CO2 reduction. The optimized Cu catalyst achieves a C2 Faradaic efficiency as high as 60.72% in the presence of merely 25% CO2, which is almost equivalent to that observed with pure CO2.

Ni-modified FeOOH integrated electrode by self-source corrosion of nickel foam for high-efficiency electrochemical water oxidation.

The construction and application of efficient iron oxyhydroxide (FeOOH) is still a challenge in the field of energy conversion. Here, a facile preparation method is developed by directly utilizing commercialized nickel foams (NF) as the nickel source and the supporting framework, as well as the ingenious use of etching effect originating from acidic medium in the process of iron salt hydrolysis. As a result, a Ni-modulated FeOOH integrated electrode (Ni-FeOOH/NF) is obtained. Unexpectedly, the implementation of our scheme effectively activates the catalytic intrinsic activity of FeOOH, successfully transforming the inert NF into an integrated electrode with high oxygen evolution reaction (OER) performance. Specifically, the Ni-FeOOH/NF exhibits the overpotential of 277 mV (@100 mA cm-2) and superior stability for OER. Additionally, the as-prepared Ni-FeOOH/NF electrode could also operate steadily for OER in alkaline adjusted saline water. Our research provides a new idea for the preparation of satisfactory Fe-based metal materials as OER electrocatalysts.

Surface Self-Transforming FeTi-LDH Overlayer in Fe2 O3 /Fe2 TiO5 Photoanode for Improved Water Oxidation.

Integrating hematite nanostructures with efficient layer double hydroxides (LDHs) is highly desirable to improve the photoelectrochemical (PEC) water oxidation performance. Here, an innovative and facile strategy is developed to fabricate the FeTi-LDH overlayer decorated Fe2 O3 /Fe2 TiO5 photoanode via a surface self-transformation induced by the co-treatment of hydrazine and NaOH at room temperature. Electrochemical measurements find that this favorable structure can not only facilitate the charge transfer/separation at the electrode/electrolyte interface but also accelerate the surface water oxidation kinetics. Consequently, the as-obtained Fe2 O3 /Fe2 TiO5 /LDH photoanode exhibits a remarkably increased photocurrent density of 3.54 mA cm-2 at 1.23 V versus reversible hydrogen electrode (RHE) accompanied by an obvious cathodic shift (≈140 mV) in the onset potential. This work opens up a new and effective pathway for the design of high-performance hematite photoanodes toward efficient PEC water oxidation.

CoMo layered double hydroxide equipped with carbon nanotubes for electrocatalytic oxygen evolution reaction.

To carry out effective resource reforming of sustainable electricity, hydrogen production by electrochemical water splitting provides an eco-friendly and economical way. Nevertheless, the oxygen evolution reaction (OER) at the anode is limited by the slow reaction process, which hinders the large-scale development and application of electrolysis technology. In this work, we present an electrocatalyst with superior OER performance, which attributed to the abundant active sites and good electronic conductivity. The two-dimensional CoMo Layered Double Hydroxide nanosheets are synthesized and deposited on conductive carbon nanotubes (CoMo LDH/CNTs), and then hybrid composites show better catalytic performance than their undecorated counterpart under identical conditions. Specifically, CoMo LDH/CNTs exhibit the low overpotential of 268 mV to obtain 10 mA cm-2and satisfactory stability (more than 40 h). We emphasize that this hybridization strategy with a conductive supporting framework could design more abundant and low-cost OER electrocatalysts to minimize electrical energy consumption, thereby achieving efficient conversion between energy sources.

Challenges and Opportunities in Electrocatalytic CO2 Reduction to Chemicals and Fuels.

The global temperature increase must be limited to below 1.5 °C to alleviate the worst effects of climate change. Electrocatalytic CO2 reduction (ECO2 R) to generate chemicals and feedstocks is considered one of the most promising technologies to cut CO2 emission at an industrial level. However, despite decades of studies, advances at the laboratory scale have not yet led to high industrial deployment rates. This Review discusses practical challenges in the industrial chain that hamper the scaling-up deployment of the ECO2 R technology. Faradaic efficiencies (FEs) of about 100 % and current densities above 200 mA cm-2 have been achieved for the ECO2 R to CO/HCOOH, and the stability of the electrolysis system has been prolonged to 2000 h. For ECO2 R to C2 H4 , the maximum FE is over 80 %, and the highest current density has reached the A cm-2 level. Thus, it is believed that ECO2 R may have reached the stage for scale-up. We aim to provide insights that can accelerate the development of the ECO2 R technology.

Modulating Built-In Electric Field via Variable Oxygen Affinity for Robust Hydrogen Evolution Reaction in Neutral Media.

Work function strongly impacts the surficial charge distribution, especially for metal-support electrocatalysts when a built-in electric field (BEF) is constructed. Therefore, studying the correlation between work function and BEF is crucial for understanding the intrinsic reaction mechanism. Herein, we present a Pt@CoOx electrocatalyst with a large work function difference (ΔΦ) and strong BEF, which shows outstanding hydrogen evolution activity in a neutral medium with a 4.5-fold mass activity higher than 20 % Pt/C. Both experimental and theoretical results confirm the interfacial charge redistribution induced by the strong BEF, thus subtly optimizing hydrogen and hydroxide adsorption energy. This work not only provides fresh insights into the neutral hydrogen evolution mechanism but also proposes new design principles toward efficient electrocatalysts for hydrogen production in a neutral medium.

Unique Dual-Sites Boosting Overall CO2 Photoconversion by Hierarchical Electron Harvesters.

Low selectivity and poor activity of photocatalytic CO2 reduction process are usually limiting factors for its applicability. Herein, a hierarchical electron harvesting system is designed on CoNiP hollow nano-millefeuille (CoNiP NH), which enables the charge enrichment on CoNi dual active sites and selective conversion of CO2 to CH4 . The CoNiP serves as an electron harvester and photonic "black hole" accelerating the kinetics for CO2 -catalyzed reactions. Moreover, the dual sites form from highly stable CoONiC intermediates, which thermodynamically not only lower the reaction energy barrier but also transform the reaction pathways, thus enabling the highly selective generation of CH4 from CO2 . As an outcome, the CoNiP NH/black phosphorus with dual sites leads to a tremendously improved photocatalytic CH4 generation with a selectivity of 86.6% and an impressive activity of 38.7 µmol g-1  h-1 .

Metal-Oxide-Mediated Subtractive Manufacturing of Two-Dimensional Carbon Nitride for High-Efficiency and High-Yield Photocatalytic H2 Evolution.

g-C3N4 is a promising visible-light-driven photocatalyst for H2 evolution reaction; however, the achievement of the high photocatalytic performance is primarily limited by the low separation efficiency of the photogenerated charge carriers and partly restricted by the slow kinetics of charge transfer. 2D g-C3N4 can significantly improve the charge generation, transfer, and separation efficiencies. The 2D g-C3N4-based Z-scheme heterostructure can further enhance the charge-carrier separation and simultaneously increase the redox ability, thereby further boosting the photocatalytic performance. Here we report a transition-metal-oxide (TMO)-mediated subtractive manufacturing process toward the large-scale synthesis of 2D g-C3N4 and the simultaneous formation of a 2D/2D TMO/g-C3N4 Z-scheme heterojunction. The TMOs serve as catalysts to facilitate the hydrolysis reaction of the bulk g-C3N4 in the presence of moist air, forming 2D g-C3N4. The resulting 2D/2D TMO/g-C3N4 catalysts, in particular, 2D/2D Co3O4/g-C3N4, exhibit high-efficiency and high-yield photocatalytic H2 evolution due to the suppression of electron-hole pair recombination and enhanced redox ability. The 2D/2D Co3O4/g-C3N4 photocatalyzes the H2 evolution with a rate of ∼370 µmol h-1 within λ > 400 nm. The external quantum efficiency of 2D/2D Co3O4/g-C3N4 at λ = 405 nm reaches 53.6%, which is among the highest values for g-C3N4-based catalysts.

Accelerating Photogenerated Charge Kinetics via the Synergetic Utilization of 2D Semiconducting Structural Advantages and Noble-Metal-Free Schottky Junction Effect.

Although photocatalysis is one of the most promising technologies for environmental and energy issues, the irreconcilable contradiction between the absorption of the visible light and the strong redox capability of the photocatalyst and the low photocatalytic reaction kinetics result in the poor efficiency. Here, a composite photocatalyst is reported with high redox capability and accelerated reaction kinetics synergistically utilizing 2D semiconducting structural advantages and the noble-metal-free Schottky junction effect. The 2D structure can not only increase the bandgap of the photocatalyst but also improve the transfer and separation of the photogenerated charge carriers. Furthermore, the introduction of the noble-metal-free Schottky junction effect accelerates the photocatalytic reaction kinetics. The Schottky barrier can also prevent the photogenerated charges trapped by the electron acceptor from flowing back to the semiconductor, which can further boost the photocatalytic performance. The transfer process of the photogenerated charge carriers is also researched in detail by the comprehensive characterization methods, which enable the photocatalytic mechanism to be revealed.

Controllable synthesized heterostructure photocatalyst Mo2C@C/2D g-C3N4: enhanced catalytic performance for hydrogen production.

Photocatalysis is a promising technology which can be applied in the fields of energy and environment. However, low charge separation efficiency has limited its commercial applications. In this work, we report a route to a controllable synthesized visible-light-driven heterostructure photocatalyst Mo2C@C/2D g-C3N4. The interfacial conductivity was improved by introducing Mo2C@C, which promoted the transportation of photogenerated carriers and suppressed their recombination. The optimal composite achieved a hydrogen (H2) generation rate of 2269.47 µmol g-1 h-1, and an external quantum efficiency (EQE) achieved 9.07% at λ = 405 nm. Thus, the great co-catalytic activity of Mo2C@C was unambiguously demonstrated.

Construction of a 2D Graphene-Like MoS2/C3N4 Heterojunction with Enhanced Visible-Light Photocatalytic Activity and Photoelectrochemical Activity.

A novel graphene-like MoS2 /C3N4 (GL-MoS2/C3N4) composite photocatalyst has been synthesized by a facile ethylene glycol (EG)-assisted solvothermal method. The structure and morphology of this GL-MoS2/C3N4 photocatalyst have been investigated by a wide range of characterization methods. The results showed that GL-MoS2 was uniformly distributed on the surface of GL-C3N4 forming a heterostructure. The obtained composite exhibited strong absorbing ability in the ultraviolet (UV) and visible regions. When irradiated with visible light, the composite photocatalyst showed high activity superior to those of the respective individual components GL-MoS2 and GL-C3N4 in the degradation of methyl orange. The enhanced photocatalytic activity of the composite may be attributed to the efficient separation of electron-hole pairs as a result of the matching band potentials between GL-MoS2 and GL-C3N4. Furthermore, a photocatalytic mechanism for the composite material has been proposed, and the photocatalytic reaction kinetics has been measured. Moreover, GL-MoS2/C3N4 could serve as a novel sensor for trace amounts of Cu(2+) since it exhibited good selectivity for Cu(2+) detection in water.

Controllable synthesis of CeO2/g-C3N4 composites and their applications in the environment.

This research has developed a photocatalytic reactor that includes circulating water, light, and a temperature control system. CeO2/g-C3N4 composites with high photocatalytic activity and stability were synthesized by a simple and facile hydrothermal method. The obtained photocatalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). It was found that in the CeO2/g-C3N4 composites, the CeO2 nanoparticles were homogeneously cubic in shape (from 3 to 10 nm) and were evenly dispersed on the surface of the g-C3N4. At constant temperature (30 °C), 5% CeO2/g-C3N4 photocatalyst showed the best photocatalytic activity for degrading organic dye methylene blue (MB) under visible light irradiation. The photocatalytic reaction for degrading MB followed first-order kinetics and 5% CeO2/g-C3N4 exhibited a higher apparent rate of 1.2686 min(-1), 7.8 times higher than that of the pure g-C3N4 (0.1621 min(-1)). In addition, it was found that 5% CeO2/g-C3N4 had a new property that it could be used as a sensor for the determination of trace amounts of Cu(2+). Such unique design and one-step synthesis, with an exposed high-activity surface, are important for both technical applications and theoretical investigations.

Graphene-analogue carbon nitride: novel exfoliation synthesis and its application in photocatalysis and photoelectrochemical selective detection of trace amount of Cu²âº.

Graphene-analogue nanostructures defined as a new kind of promising materials with unique electronic, surface and optical properties have received much attention in the fields of catalysis, energy storage, sensing and electronic devices. Due to the distinctive structure characteristics of the graphene-analogue materials, they brought novel and amazing properties. Herein, graphene-analogue carbon nitride (GA-C3N4) was synthesized by high-yield, large-scale thermal exfoliation from the graphitic C3N4-based intercalation compound. Graphene-analogue carbon nitride exhibited 2D thin-layer structure with 6-9 atomic thickness, a high specific surface area of 30.1 m(2) g(-1), increased photocurrent responses and improved electron transport ability, which could give rise to enhancing the photocatalytic activity and stability. The graphene-analogue carbon nitride had a new features that could make it suitable as a sensor for Cu(2+) determination. So GA-C3N4 is a new but promising candidate for heavy metal ions (Cu(2+)) determination in water environment. The photocatalytic mechanism and photoelectrochemical selective sensing of Cu(2+) were also discussed.