Economical water electrolysis requires highly active non-noble electrocatalysts to overcome the sluggish kinetics of the two half-cell reactions, oxygen evolution reaction, and hydrogen evolution reaction. Although intensive efforts have been committed to achieve a hydrogen economy, the expensive noble metal-based catalysts remain under consideration. Therefore, the engineering of self-supported electrocatalysts prepared using a direct growth strategy on three-dimensional (3D) nickel foam (NF) as a conductive substrate has garnered significant interest. This is due to the large active surface area and 3D porous network offered by these electrocatalysts, which can enhance the synergistic effect between the catalyst and the substrate, as well as improve electrocatalytic performance. Hydrothermal-assisted growth, microwave heating, electrodeposition, and other physical methods (i.e., chemical vapor deposition and plasma treatment) have been applied to NF to fabricate competitive electrocatalysts with low overpotential and high stability. In this review, recent advancements in the development of self-supported electrocatalysts on 3D NF are described. Finally, we provide future perspectives of self-supported electrode platforms in electrochemical water splitting.
Currently, the electrochemical CO2 reduction reaction (CO2RR) can realize the resource conversion of CO2, which is a promising approach to carbon resource use. Important advancements have been made in exploring the CO2RR performance and mechanism because of the rational design of electrolyzer systems, such as H-cells, flow cells, and catalysts. Considering the future development direction of this technology and large-scale application needs, membrane electrode assembly (MEA) systems can improve energy use efficiency and achieve large-scale CO2 conversion, which is considered the most promising technology for industrial applications. This review will concentrate on the research progress and present situation of the MEA component structure. This paper begins with the composition and construction of a gas diffusion electrode. Then, the application of ion-exchange membranes in MEA is introduced. Furthermore, the effects of pH and the anion and cation of the anolyte on MEA performance are explored. Additionally, we present the anode reaction type in MEA. Finally, the challenges in this field are summarized, and upcoming trends are projected. This review should offer researchers a clearer picture of MEA systems and provide important, timely, and valuable insights into rational electrolyzer design to facilitate further development of CO2 electrochemical reduction.
Deep degradation of organic pollutants by sunlight-induced coupled photocatalytic and Fenton (photo-Fenton) reactions is of immense importance for water purification. In this work, we report a novel bifunctional catalyst (Fe-PEI-CN) by codoping graphitic carbon nitride (CN) with polyethyleneimine ethoxylated (PEI) and Fe species, which demonstrated high activity during p-chlorophenol (p-ClPhOH) degradation via H2O2 from the photocatalytic process. The relationship between the catalytic efficiency and the structure was explored using different characterization methods. The Fe modification of CN was achieved through Fe–N coordination, which ensured high dispersion of Fe species and strong stability against leaching during liquid-phase reactions. The Fe modification initiated the Fenton reaction by activating H2O2 into ·OH radicals for deep degradation of p-ClPhOH. In addition, it effectively promoted light absorption and photoelectron–hole (e–h+) separation, corresponding to improved photocatalytic activity. On the other hand, PEI could significantly improve the ability of CN to generate H2O2 through visible light photocatalysis. The maximum H2O2 yield reached up to 102.6 μmol/L, which was 22 times higher than that of primitive CN. The cooperation of photocatalysis and the self-Fenton reaction has led to high-activity mineralizing organic pollutants with strong durability, indicating good potential for practical application in wastewater treatment.
Extensive work on a Cu-modified TiO2 photocatalyst for CO2 reduction under visible light irradiation was conducted. The structure of the copper cocatalyst was established using UV–vis diffuse reflectance spectroscopy, high-resolution transmission electron microscopy, X-ray absorption spectroscopy, and X-ray photoelectron spectroscopy. It was found that copper exists in different states (Cu0, Cu+, and Cu2+), the content of which depends on the TiO2 calcination temperature and copper loading. The optimum composition of the cocatalyst has a photocatalyst based on TiO2 calcined at 700 °C and modified with 5 wt% copper, the activity of which is 22 µmol/(h·gcat) (409 nm). Analysis of the photocatalysts after the photocatalytic reaction disclosed that the copper metal on the surface of the calcined TiO2 was gradually converted into Cu2O during the photocatalytic reaction. Meanwhile, the metallic copper on the surface of the noncalcined TiO2 did not undergo any transformation during the reaction.
In recent times, lithium-ion batteries have been widely used owing to their high energy density, extended cycle lifespan, and minimal self-discharge rate. The design of high-speed rechargeable lithium-ion batteries faces a significant challenge owing to the need to increase average electric power during charging. This challenge results from the direct influence of the power level on the rate of chemical reactions occurring in the battery electrodes. In this study, the Taguchi optimization method was used to enhance the average electric power during the charging process of lithium-ion batteries. The Taguchi technique is a statistical strategy that facilitates the systematic and efficient evaluation of numerous experimental variables. The proposed method involved varying seven input factors, including positive electrode thickness, positive electrode material, positive electrode active material volume fraction, negative electrode active material volume fraction, separator thickness, positive current collector thickness, and negative current collector thickness. Three levels were assigned to each control factor to identify the optimal conditions and maximize the average electric power during charging. Moreover, a variance assessment analysis was conducted to validate the results obtained from the Taguchi analysis. The results revealed that the Taguchi method was an effective approach for optimizing the average electric power during the charging of lithium-ion batteries. This indicates that the positive electrode material, followed by the separator thickness and the negative electrode active material volume fraction, was key factors significantly influencing the average electric power during the charging of lithium-ion batteries response. The identification of optimal conditions resulted in the improved performance of lithium-ion batteries, extending their potential in various applications. Particularly, lithium-ion batteries with average electric power of 16 W and 17 W during charging were designed and simulated in the range of 0–12000 s using COMSOL Multiphysics software. This study efficiently employs the Taguchi optimization technique to develop lithium-ion batteries capable of storing a predetermined average electric power during the charging phase. Therefore, this method enables the battery to achieve complete charging within a specific timeframe tailored to a specific application. The implementation of this method can save costs, time, and materials compared with other alternative methods, such as the trial-and-error approach.
Photoelectrochemical (PEC) small-molecule oxidation can selectively transform substrates into high-value-added fine chemicals and increase the rate of cathode hydrogen evolution. Nevertheless, achieving high-selectivity PEC oxidation of small molecules to produce specific products is a very challenging task. In general, selectivity can be improved by changing the surface catalytic sites of the photoanode and modulating the interfacial environments of the reactions. Herein, recent advances in approaches to improving selective PEC oxidation of small molecules are introduced. We first briefly discuss the basic concept and fundamentals of small-molecule PEC oxidation. The reported approaches to improving the performance of selective PEC oxidation of small molecules are highlighted from two aspects: (1) changing the surface properties of photoanodes by selecting suitable materials or modifying the photoanodes and (2) mediating the oxidation reactions using redox mediators. The PEC oxidation mechanism of these studies is emphasized. We also discuss the challenges in this research direction and offer a perspective on the further development of selective PEC-based small-molecule transformation.
Capturing and utilizing CO2 from the production process is the key to solving the excessive CO2 emission problem. CO2 hydrogenation with green hydrogen to produce olefins is an effective and promising way to utilize CO2 and produce valuable chemicals. The olefins can be produced by CO2 hydrogenation through two routes, i.e., CO2-FTS (carbon dioxide Fischer–Tropsch synthesis) and MeOH (methanol-mediated), among which CO2-FTS has significant advantages over MeOH in practical applications due to its relatively high CO2 conversion and low energy consumption potentials. However, the CO2-FTS faces challenges of difficult CO2 activation and low olefins selectivity. Iron-based catalysts are promising for CO2-FTS due to their dual functionality of catalyzing RWGS and CO-FTS reactions. This review summarizes the recent progress on iron-based catalysts for CO2 hydrogenation via the FTS route and analyzes the catalyst optimization from the perspectives of additives, active sites, and reaction mechanisms. Furthermore, we also outline principles and challenges for rational design of high-performance CO2-FTS catalysts.
The study focused on the modification with platinum of dark defective titania obtained via pulsed laser ablation. Both the method of Pt introduction and the nature of the Pt precursor were varied. All samples exhibited similar phase compositions, specific surface areas, and Pt contents. High-resolution transmission electron microscopy coupled with pulsed CO adsorption revealed increased dispersity when photoreduction and the hydroxonitrate complex (Me4N)2[Pt2(OH)2(NO3)8] were used. The sample featured a high content of single-atom species and subnano-sized Pt clusters. The X-ray photoelectron spectroscopy results showed that the photoreduction method facilitated the appearance of a larger number of Pt2+ states, which appeared owing to the strong metal–support interaction (SMSI) effect of the transfer of electron density from the electron-saturated defects on the TiO2 surface to Pt4+. In the hydrogen evolution reaction, samples with a significant fraction of the Pt2+ ionic component, capable of generating short-lived Pt0 single-atom sites under irradiation due to the SMSI effect, exhibited the highest photocatalytic activity. The 0.5Pt(C)/TiO2–Ph sample exhibited the highest hydrogen yield with a quantum efficiency of 0.53, retaining its activity even after 8 h of operation.