Pore-Scale Investigation of Coupled Two-Phase and Reactive Transport in the Cathode Electrode of Proton Exchange Membrane Fuel Cells

A three-dimensional multicomponent multiphase lattice Boltzmann model (LBM) is established to model the coupled two-phase and reactive transport phenomena in the cathode electrode of proton exchange membrane fuel cells. The gas diffusion layer (GDL) and microporous layer (MPL) are stochastically reconstructed with the inside dynamic distribution of oxygen and liquid water resolved, and the catalyst layer is simplified as a superthin layer to address the electrochemical reaction, which provides a clear description of the flooding effect on mass transport and performance. Different kinds of electrodes are reconstructed to determine the optimum porosity and structure design of the GDL and MPL by comparing the transport resistance and performance under the flooding condition. The simulation results show that gradient porosity GDL helps to increase the reactive area and average concentration under flooding. The presence of the MPL ensures the oxygen transport space and reaction area because liquid water cannot transport through micropores. Moreover, the MPL helps in the uniform distribution of oxygen for an efficient in-plane transport capacity. Crack and perforation structures can accelerate the water transport in the assembly. The systematic perforation design yields the best performance under flooding by separating the transport of liquid water and oxygen.

Manganese-Based Catalysts for Indoor Volatile Organic Compounds Degradation with Low Energy Consumption and High Efficiency

With the development of industrialization, the emission of volatile organic compounds (VOCs) to atmosphere causes serious environmental problems and the treatment of VOCs needs to consume a lot of energy. Moreover, indoor VOCs are seriously harmful to human health. Thus, there is an urgent requirement for the development of indoor VOCs treatment technologies. Catalytic degradation of VOCs, as a low energy consumption, high efficiency, and easy to achieve manner, has been widely studied in related fields. As a kind of transition metal catalyst, manganese-based catalysts have attracted a lot of attention in the catalytic degradation of VOCs because of their unique advantages including high efficiency, low cost, and excellent stability. This paper reviews the state-of-the-art progress of manganese-based catalysts for VOCs catalytic degradation. We introduce the thermocatalytic, photocatalytic and photo-thermocatalytic degradation of VOCs on manganese-based catalysts in this paper. The optimization of manganese-based catalysts by means of structural design, decorating modification and defect engineering is discussed. Graphical Abstract

Comparative Electrocatalytic Oxygen Evolution Reaction Studies of Spinel NiFe2O4 and Its Nanocarbon Hybrids

Electrocatalytic oxygen evolution reaction (OER) is one of the crucial reactions for converting renewable electricity into chemical fuel in the form of hydrogen. To date, there is still a challenge in designing ideal cost-effective OER catalysts with excellent activity and robust durability. The hybridization of transition metal oxides and carbonaceous materials is one of the most effective and promising strategies to develop high-performance electrocatalysts. Herein, this work synthesized hybrids of NiFe2O4 spinel materials with two-dimensional (2D) graphene oxide and one-dimensional (1D) carbon nanotubes using a facile solvothermal approach. Electrocatalytic activities of NiFe2O4 with 2D graphene oxide toward OER were realized to be superior even to the 1D carbon nanotube-based electrocatalyst in terms of overpotential to reach a current density of 10 mA/cm2 as well as Tafel slopes. The NiFe2O4 with 2D graphene oxide hybrid exhibits good stability with an overpotential of 327 mV at a current density of 10 mA/cm2 and a Tafel slope of 103 mV/dec. The high performance of NiFe2O4 with 2D graphene oxide is mainly attributed to its unique morphology, more exposed active sites, and a porous structure with a high surface area. Thus, an approach of hybridizing a metal oxide with a carbonaceous material offers an attractive platform for developing an efficient electrocatalyst for water electrochemistry applications.

One-Step Hydrothermal Synthesis of a CoTe@rGO Electrode Material for Supercapacitors

CoTe@reduced graphene oxide (CoTe@rGO) electrode materials for supercapacitors were prepared by a one-step hydrothermal method in this paper. Compared with that of pure CoTe, the electrochemical performance of CoTe@rGO was significantly improved. The results showed that the optimal CoTe@rGO electrode material has a remarkably high specific capacitance of 810.6 F/g at a current density of 1 A/g. At 5 A/g, the synthesized material retained 77.2% of its initial capacitance even after 5000 charge/discharge cycles, thereby demonstrating good cycling stability. Moreover, even at a high current density of 20 A/g, the composite electrode retained 79.0% of its specific capacitance at 1 A/g, thus confirming its excellent rate performance. An asymmetric supercapacitor (ASC) with a wider potential window and higher energy density was assembled by using 3 M KOH as the electrolyte, the CoTe@rGO electrode as the positive electrode, and active carbon as the negative electrode. The operating voltage of the supercapacitor could be increased to 1.6 V, and its specific capacitance could reach 112.6 F/g at 1 A/g. The specific capacitance retention rate of the fabricated supercapacitor after 5000 charge/discharge cycles at 5 A/g was 87.1%, which confirms its excellent cycling stability. In addition, the ASC revealed a high energy density of 40.04 W·h/kg at a power density of 799.91 W/kg and a high power density of 4004.93 W/kg at an energy density of 33.43 W·h/kg. These results collectively show that CoTe@rGO materials have broad application prospects.

Electroreduction of Carbon Dioxide by Heterogenized Cofacial Porphyrins

Great attention has been paid to cofacial porphyrins due to their many unique advantages over their monomeric analogs. However, their synthesis is usually complicated. In this work, a facile impregnation method for preparing heterogenized, cofacially stacked porphyrins is proposed. An anionic porphyrin is introduced as an underlayer for immobilization of cationic cobalt porphyrin via electrostatic force. The metal center of the underlying molecule contributes to the electronic structure of the upper cationic cobalt porphyrin. Screening reveals the anionic iron porphyrin to be the most efficient underlayer molecule, lowering the activation energy barrier of CO2 electroreduction, with an improved turnover frequency by 74% to 8.0 s−1 at − 0.6 V versus RHE.

Visible Light-Responsive N-Doped TiO2 Photocatalysis: Synthesis, Characterizations, and Applications

Photocatalysis based on semiconductors has recently been receiving considerable research interest because of its extensive applications in environmental remediation and renewable energy generation. Various semiconductor-based materials that are vital to solar energy utilization have been extensively investigated, among which titanium oxide (TiO2) has attracted considerable attention because of its exceptional physicochemical characteristics. However, the sluggish responsiveness to visible light in the solar spectrum and the inefficient separation of photoinduced electron–hole pairs hamper the practical application of TiO2 materials. To overcome the aforementioned serious drawbacks of TiO2, numerous strategies, such as doping with foreign atoms, particularly nitrogen (N), have been improved in the past few decades. This review aims to provide a comprehensive update and description of the recent developments of N-doped TiO2 materials for visible light-responsive photocatalysis, such as (1) the preparation of N-doped/co-doped TiO2 photocatalysts and (2) mechanistic studies on the reasons for visible light response. Furthermore, the most recent and significant advances in the field of solar energy applications of modified N-doped TiO2 are summarized. The analysis indicated the critical need for further development of these types of materials for the solar-to-energy conversion, particularly for water splitting purposes.

Recent Developments of Antimony-Based Anodes for Sodium- and Potassium-Ion Batteries

The development of sodium-ion (SIBs) and potassium-ion batteries (PIBs) has increased rapidly because of the abundant resources and cost-effectiveness of Na and K. Antimony (Sb) plays an important role in SIBs and PIBs because of its high theoretical capacity, proper working voltage, and low cost. However, Sb-based anodes have the drawbacks of large volume changes and weak charge transfer during the charge and discharge processes, thus leading to poor cycling and rapid capacity decay. To address such drawbacks, many strategies and a variety of Sb-based materials have been developed in recent years. This review systematically introduces the recent research progress of a variety of Sb-based anodes for SIBs and PIBs from the perspective of composition selection, preparation technologies, structural characteristics, and energy storage behaviors. Moreover, corresponding examples are presented to illustrate the advantages or disadvantages of these anodes. Finally, we summarize the challenges of the development of Sb-based materials for Na/K-ion batteries and propose potential research directions for their further development.