As a highly appealing technology for hydrogen generation, water electrolysis including oxygen evolution reaction (OER) at the anode and hydrogen evolution reaction (HER) at the cathode largely ...depends on the availability of efficient electrocatalysts. Accordingly, over the past years, much effort has been made to develop various electrocatalysts with superior performance and reduced cost. Among them, ruthenium (Ru)-based materials for OER and HER are very promising because of their prominent catalytic activity, pH-universal application, the cheapest price among the precious metal family, and so on. Herein, recent advances in this hot research field are comprehensively reviewed. A general description about water splitting is presented to understand the reaction mechanism and proposed scaling relations toward activities, and key stability issues for Ru-based materials are further given. Subsequently, various Ru-involving electrocatalysts are introduced and classified into different groups for improving or optimizing electrocatalytic properties, with a special focus on several significant bifunctional electrocatalysts along with a simulated water electrolyzer. Finally, a perspective on the existing challenges and future progress of Ru-based catalysts toward OER and HER is provided. The main aim here is to shed some light on the design and construction of emerging catalysts for energy storage and conversion technologies.
In order to improve the photo-to-electric energy conversion efficiency, a hybrid system is proposed by integrating a thermoelectric generator (TEG) with a perovskite solar cell (PSC). According to ...the derived formulas for the efficiency and power output of the hybrid system, three especial work states such as opened TEG, opened PSC, and PSC-TEG tandem cells are, respectively, discussed through numerical simulation. Further, we study the general work state, i.e., the PSC and the TEG independently drive their loads and are coupled with each other through energy balance equation. The matching loads 0.13Ωand 12.3Ωof the two subsystems and the optimum area 0.0324 m2 of the PSC can be chosen to obtain the maximum efficiency 0.216. Moreover, the perovskite layer’s optimum thickness 449.7nmis designed to obtain the overall maximum efficiency 0.229. For comparison, the hybrid system achieves improved overall energy efficiency by harnessing the waste heat produced in the PSC. The proposed model may provide some theoretical bases for the optimal design of practical PSC–TEG hybrid systems.
•A PSC-TEG hybrid system is proposed to decrease thermal loss and improve efficiency.•The maximum efficiency of the single PSC 0.204 is achieved as the TEG is opened.•The maximum efficiency of the single TEG 0.0516 is obtained as the PSC is opened.•The maximum efficiency is 0.229 at the PSC and TEG independent work state.•Performances of the tandem cells in present work are compared to the reported work.
Eu-type generalized hydrodynamic equations have been derived from the Boltzmann kinetic theory and applied to investigate continuum and/or rarefied gas flows. This short communication first reports ...detailed and important issues in the use of the mixed discontinuous Galerkin method to solve Eu-type generalized hydrodynamic equations in multidimensions. Three major issues are reported. These include the treatment of solid boundary conditions for the nonlinear constitutive equations, a slope limiter to maintain high accuracy and avoid unphysical oscillations, and the computational efficiency compared with that of the particle method. In addition, we implement the present model to a rigid problem, which includes gas flows around the NACA0018 airfoil, a sharp wedge, a sphere and a three-dimensional Apollo configuration.
Development of noble-metal-free materials with remarkable electrocatalytic water-splitting performance in acidic or neutral media has sparked considerable attention in recent years. Herein, we review ...the latest research on design and fabrication of precious-metal-free catalytic materials for overall water electrolysis in non-alkaline environment, especially highlighting several optimizing approaches to enhance the catalytic behavior and to realize effective bifunctional electrocatalysts. All these involved noble-metal-free electrocatalysts are classified into transition-metal oxides (TMOs), transition-metal nitrides (TMNs), transition-metal carbides (TMCs), transition-metal phosphides (TMPs), transition-metal chalcogenides, metal complexes, and metal-free carbons, as shown in the main part. Besides, the paper also offers an introduction of the fundamental electrochemistry of water splitting before entering the subject, as well as a prospective discussion on mechanism understanding, novel catalysts fabrication, and standardized performance measurements/evaluation in the last section.
Display omitted
Thermal management in solid oxide fuel cells (SOFC) is a critical issue due to non-uniform electrochemical reactions and convective flows within the cells. Therefore, a 2D mathematical model is ...established herein to investigate the thermal responses of a tubular methanol-fueled SOFC. Results show that unlike the low-temperature condition of 873 K, where the peak temperature gradient occurs at the cell center, it appears near the fuel inlet at 1073 K because of the rapid temperature rise induced by the elevated current density. Despite the large heat convection capacity, excessive air could not effectively eliminate the harmful temperature gradient caused by the large current density. Thus, optimal control of the current density by properly selecting the operating potential could generate a local thermal neutral state. Interestingly, the maximum axial temperature gradient could be reduced by about 18% at 973 K and 20% at 1073 K when the air with a 5 K higher temperature is supplied. Additionally, despite the higher electrochemical performance observed, the cell with a counter-flow arrangement featured by a larger hot area and higher maximum temperature gradients is not preferable for a ceramic SOFC system considering thermal durability. Overall, this study could provide insightful thermal information for the operating condition selection, structure design, and stability assessment of realistic SOFCs combined with their internal reforming process.
•Different optimized electrode is designed for redox flow batteries.•The correlation between electrode design and flow field pattern is studied.•The modified electrode has an effective range for ...voltage improvement.
The fibrous electrode is an essential component of the redox flow batteries, as the electrode structure influences the reactant/product local concentration, electrochemical reaction kinetics, and the pressure loss of the battery. A three-dimensional numerical model of vanadium redox flow battery (VRFB) was developed in this work. After model validation, simulations were conducted to understand the effects of electrode structural parameters on the battery performance. The gradient electrode design, specific surface area, porosity, and different flow fields were studied and optimized. The results show that in the large-size VRFB system, ensuring a large porosity can minimize the concentration polarization, which not only improves the battery performance, and also reduce the pressure loss. To further improve the mass transfer, fibers with larger diameter can be used, and the specific surface area of the electrode can be increased by modifying the surface of the fiber. The battery performance can be significantly improved with increasing specific surface area when the specific surface area is lower than 500,000. However, with further increase in specific surface area, the voltage of the battery remains almost constant at about 1.37 V. Its influence on interdigitated flow channel case is mainly in reducing pressure loss, and on serpentine flow channel case is directly reflected in improving battery performance.
•A three-dimensional non-isothermal model of HT-PEMFC was developed.•Thickness and porosity of gas diffusion layer were studied.•Flow uniformity, diffusion flux and ohmic resistance were ...examined.•Optimal values of thickness and porosity were proposed.•A performance increment of 7.7% was achieved.
Wide ranges of thickness (e.g. 100–400 μm) and porosity (e.g. 30–70%) of gas diffusion layer (GDL) in a high temperature proton exchange membrane fuel cell (HT-PEMFC) are available in the literature. However, the effects of GDL porosity and thickness on electron conduction and gas distribution uniformity (under the rib and under the channel) are unclear. In this study, a numerical non-isothermal 3D model was developed. After model validation, parametric analyses were performed to investigate the effects of thickness and porosity on flow uniformity (under the rib and under the channel), diffusion flux and ohmic resistance. It is found that both the flow uniformity and ohmic resistance increase with increasing thickness and porosity. However, the thickness and porosity have opposite influence on diffusion flux, which decreases with increasing GDL thickness but increases with increasing porosity. Unlike the previous research suggesting thin GDL with high porosity, optimal GDL thickness and porosity are found in the present study. The appropriate GDL thicknesses for anode and cathode are 80–120 μm and 140–170 μm respectively while the optimal value for GDL porosity is 35–45%. This study clearly demonstrates that we can further achieve a performance increment of 7.7% by carefully controlling the thickness and porosity of GDL.
•A 2D model is developed for the methanol-fuelled SOFC.•Addition of steam helps inhibit carbon deposition but decreases SOFC performance.•The temperature distribution in the SOFC is substantially ...influenced by the operating conditions.•A higher temperature is beneficial to improve the SOFC power output and temperature uniformity.
Methanol is a promising fuel for the solid oxide fuel cell (SOFC) due to its easy storage and transportation compared with hydrogen. As no thermo-electrochemical modelling study has been conducted on methanol-fuelled SOFC, a 2D model is developed to simulate the methanol decomposition reaction, water gas shift reaction, electrochemical reactions, heat and mass transfer processes in the methanol-fuelled SOFC. After model validation, parametric simulations are performed to investigate the effects of the operating potential, steam to carbon ratio, the inlet temperature and fuel/air flow rates on the performance of SOFCs. At 1073 K, the peak power density of methanol-fuelled SOFC is higher than 10000 W m−2 with the steam to carbon ratio of 1. In addition, the temperature distribution in SOFC could be remarkably affected by the working conditions due to the chemical/electrochemical reactions and overpotential losses. Large temperature variation (nearly 180 K) between the inlet and outlet of the SOFC is observed mainly due to greatly improved current density at low operating potential. Also, temperature reduction can be achieved by increasing the steam to carbon ratio and gas flow rates (higher than 170 SCCM for air and 0.1 ml min−1 for fuel mixture, respectively), which could improve the long-term stability from the perspective of the thermal stress but inevitably lower the efficiency of the SOFC. Meanwhile, higher inlet temperature not only enhances the power output, but improves the uniformity of the cell temperature distribution. Overall, the investigations of the present study could serve as a solid guidance to understand the thermal characteristics of solid oxide fuel cells running on mixture of the steam and methanol.
The rib size is a critical engineering design parameter for high temperature proton exchange membrane fuel cell (HT-PEMFC) stack development, yet it hasn't been studied for HT-PEMFC. A ...three-dimensional, non-isothermal model was developed in this work to investigate the effect of channel to rib width ratios (CRWR) on the performance of HT-PEMFC. The reaction heat caused by entropy change was divided into cathodic half-reaction heat and anodic half-reaction heat. The results show that the ratio value significantly influence the gas diffusion, electron conduction and the distribution of current density in the porous electrodes. Increasing this ratio facilitates gas transport in the porous electrode but causes higher ohmic loss due to longer distance for electron conduction. As a result, an optimal ratio of about 1 is observed, which results in a peak power density of 0.428 W/cm2. High current density is observed under the channel with a small ratio value while a high ratio value would cause high current density to appear under the rib, signifying the rib size effect on electrochemical behavior of HT-PEMFC. Apart from the electrical power output, the CRWR value also greatly influences the fluid flow and temperature distribution inside the cell, which would influence the long-term stability of HT-PEMFC. In the subsequent studies, efforts will be made to develop new stack configurations with more uniform gas distribution, short electron conduction path and low temperature gradient.
•A three-dimensional non-isothermal model of HT-PEMFC is developed.•Effects of channel to rib width ratio on different cell behaviours are investigated.•A peak power density of 0.428 W/cm2 is observed with an optimal ratio of about 1.
Interconnector (IC) is a critical component of solid oxide fuel cell (SOFC) stack for current collection and gas distribution. However, the commonly used IC design causes low average SOFC stack ...performance due to the highly uneven distribution of gas (especially O2) in the porous electrodes and the contact resistance between IC and electrode. In this study, several unconventional IC designs are proposed and studied numerically by 3D multi-physics modeling. Compared with the traditional straight channel-based IC design, the new IC design can achieve more uniform distribution of O2 in the cathode of SOFC. As a result, the peak power density of SOFC can be improved by up to 27.86%. The performance improvement can be attributed to the discrete distribution of ribs, the reduction of rib size, and the spatial layout arrangement of discrete ribs, which may shorten gas diffusion path, current collection path, or both. It is also found that the performance degradation caused by IC oxidation is highly related to the contact area between IC and electrode. In addition, the increased parasitic power loss induced by the newly designed IC is less than 0.1% of the increased electric power, so it can be neglected.
•New IC designs are proposed to enhance electric performance.•Contact resistance and contact area are considered for IC design.•The uniformity of oxygen concentration is improved by the newly designed ICs.•Electrical power and peak power density boosted significantly by proper IC design.•Performance degradation is evaluated considering IC oxidation.
PDF
