Proton exchange membrane fuel cell (PEMFC) is a crucial route for energy saving, emission reduction, and the development of new energy vehicles because of its high power density, high energy density, as well as the low operating temperature which corresponds to fast starting and power matching. However, the rare and expensive Pt resource greatly hinders the mass production of the fuel cell, and the development of highly active and durable non-precious metal catalysts toward the oxygen reduction reaction (ORR) in the cathode is considered to be the ultimate solution. In this article, a highly active and durable Fe-N-C catalyst was facilely derived from metal-organic framework (MOF) materials, and a favorable structure of carbon nanotubes (CNTs) was formed, which accounts for a desired good durability. The as-optimized catalyst has a half-wave potential of 0.84 V for the ORR, which is comparable to that of commercial Pt/C. More attractively, it has good stabilities both in rotating disk electrode (RDE) and single-cell tests, which provides a large practical application potential in the replacement of Pt catalyst as the ORR electrocatalyst in fuel cells.

The gas flow of carbon dioxide from the catalyst layer (CL) through the microporous layer (MPL) and gas diffusion layer (GDL) has great impacts on the water and fuel management in direct methanol fuel cells (DMFCs). This work has developed a liquid–vapor two-phase model considering the counter flow of carbon dioxide gas, methanol, and water liquid solution in porous electrodes of DMFC. The model simulation includes the capillary pressure as well as the pressure drop due to flow resistance through the fuel cell components. The pressure drop of carbon dioxide flow is found to be about two to three orders of magnitude higher than the pressure drop of the liquid flow. The big difference between liquid and gas pressure drops can be explained by two reasons: volume flowrate of gas is three orders of magnitude higher than that of liquid; only a small fraction of pores (<5%) in hydrophilic fuel cell components are available for gas flow. Model results indicate that the gas pressure and the mass transfer resistance of liquid and gas are more sensitive to the pore size distribution than the thickness of porous components. To buildup high gas pressure and high mass transfer resistance of liquid, the MPL and CL should avoid micro-cracks during manufacture. Distributions of pore size and wettability of the GDL and MPL have been designed to reduce the methanol crossover and improve fuel efficiency. The model results provide design guidance to obtain superior DMFC performance using highly concentrated methanol solutions or even pure methanol.

Constructing the ordered catalyst layer is one of the most effective strategies to maximize the catalyst utilization in direct methanol fuel cells (DMFCs). To gain insight into the mass and charge transports in ordered catalyst layer, herein, a two-dimensional two-phase mass-transport model involving Knudsen diffusion was proposed. It is found that the simulation results of the model with Knudsen diffusion are more consistent with the experimental results than that of the model without Knudsen diffusion. It has been demonstrated that higher porosity near the oxygen diffusion layer facilitates the oxygen transport, and the optimal porosity is obtained by balancing mass and charge transport resistances in the ordered catalyst layer. In contrast, higher catalyst loading near membrane improves the cell performance significantly. The highest peak power density of 56.5 mW/cm 2 is achieved, when the catalyst loading of the outer and inner layer is 0.15 mg/cm 2 and 0.85 mg/cm 2 , respectively.

The electrochemical reaction inside a high-power fuel cell generates a lot of heat. Excessive heat affects the performance of the membrane, so it is necessary to introduce coolant. The main objective of coolant is regulating the temperature of relatively high-power proton exchange membrane fuel cell (PEMFC) stacks efficiently. The coolant channel has a great influence on the performance of PEMFC. In this work, a multiphase, 3D PEMFC model with serpentine flow channel is developed. In order to rank structural parameters according to the degree of influence on fuel cell performance, this study analyzed the current density, O 2 mass fraction, and the distributions of temperature based on an orthogonal test scheme with three factors and three levels. The results show that rib width between the reactant flow channel and the cooling channel has the greatest influence on the current density, and gas flow channel width has the least influence.

A stable three-dimensional glucose/oxygen enzymatic biofuel cell is fabricated based on the method of polymer encapsulation-based immobilization. And three-dimensional carbon felt is used as the substrate of the bio-electrode for increasing enzymatic loading density. Gold nanoparticles and multi-wall carbon nanotubes are employed to promote direct electron transfer and enhance conductivity and electron conduction rate of bio-electrodes. Glucose dehydrogenase and bilirubin oxidase are immobilized with tetrabutylammonium bromide (TBAB) modified Nafion, which enhances the stability of the bio-electrodes by the immobilization method. A membrane-free glucose/oxygen biofuel cell is assembled with a high open-circuit voltage of 0.85 V and a maximum power density of 21.9 ± 0.1 μW/cm 2 in 0.1 M pH 7.0 phosphate buffer solution with 100 mM glucose and air saturation. And the biofuel cell shows high stability to the condition. After 60 days of periodic storage experiments, the performance of the enzymatic biofuel cell still maintained 90.3% of its electrochemical performance.

The severe corrosion of carbon supports in harsh fuel cell conditions has attracted the development of ceramic-based catalyst supports. Platinum nanoparticles supported on the carbon nanodots (CNDs)-titania (TiO 2 ) composite were synthesized in three steps: Firstly, an inorganic support, titania (TiO 2 ) was synthesized by a hydrolysis method. Secondly, the (CNDs-titania) nanocomposite support was prepared by sonicating pre-synthesized carbon nanodots (CNDs) and TiO 2 in equal volumes of ethylene glycol/water solution. Lastly, nanosized Pt particles were deposited onto the CNDs-titania composite by a polyol method to form a platinum/(CNDs-titania nanocatalyst. X-ray photoelectron spectroscopy (XPS), transmission electron microscope (TEM), and X-ray difractommetry (XRD) were used to study surface morphology of the synthesized materials. Platinum loading onto the (CNDs-titania) composite support was quantified by ICP-OES. The electrooxidation of alcohol fuels was investigated in acidic electrolytes using chronoamperometric and voltammetric techniques. It was noted that the addition of TiO 2 increases electroactivity of the nanocatalysts. The platinum/(CNDs-titania) nanocatalyst exhibited superior electroactivity during methanol and ethanol electrooxidation compared to the platinum/CNDs and Pt/C benchmark standards. Chronoamperometry (CA) curves showed that the platinum/(CNDs-titania) nanocatalyst exhibited outstanding anti-poisoning properties relative to the platinum/CNDs and commercial Pt/C nanocatalysts.

Carbon fiber paper (CFP) is currently the main product of the macroporous substrate (MPS) for the gas diffusion layer (GDL) of proton exchange membrane fuel cells (PEMFCs). The optimization of certain mechanical properties, electrical conductivity, thermal conductivity, air conduction, and mass transfer capabilities together with matched interaction can improve the core competitiveness of CFP. The artical conducts a detailed theoretical analysis of these conducting processes and principles based on CFP's main functions mentioned above. Thinner CFP with a wider pore channel brings about better mass permeability but unsatisfactory mechanical property. Thicker CFP with higher porosity and rougher surface results in worse electrical and thermal conductivity. Meanwhile, the temperature, pressure, time, and other fabrication parameters of CFP are also discussed. With so many contradictories, how to make a balance for real PEMFCs operation and reduce the cost would be a practical strategy for the optimization of CFP in the future.

Despite many efforts and improvements over the last few decades, two of the major challenges facing solid oxide fuel cells (SOFCs) are slow heating rates to operating temperature (typically < 5 °C · min −1 ) and a limited ability to thermal cycle (<200 cycles). Recently, a novel hybrid setup that combines a fuel-rich combustion reformer with a SOFC was developed and utilized to investigate rapid heating, cooling, and thermal cycling of a micro-tubular SOFC. In this work, 3000 moderate thermal cycles are conducted at a heating rate exceeding 140 °C · min −1 and a cooling rate that exceeded 100 °C · min −1 . The open-circuit voltage (OCV) was analyzed over the 150 h test, and a low degradation rate of ∼0.0008 V per 100 cycles per fuel cell was observed in the absence of the current collector degradation. Unlike a previous test, which was conducted at lower temperatures, significant degradation of the current collector was observed during this test. Electrochemical impedance spectroscopy shows that degradation in the SOFC was due to increases in ohmic losses, activation losses at the cathode, and increased concentration losses.

The world’s present reserves in terms of fossil fuels are exhausting speedily. Such rapid energy consumption can be caused of unsustainable worldwide progress. Therefore, the researcher’s challenge is to identify the most efficient and economical energy conversion method to provide a viable replacement for the ongoing conventional energy converters. In this context, fuel cell technology (solid oxide fuel cells (SOFCs)) can play a key role and convert hydrocarbon energy into electrical energy. The conventional electrolyte YSZ based SOFCs work at high temperature ∼1000 °C. In this present research, the new ceramics electrolytes materials boron doped ceria (BDC) have been developed by auto-combustion technique. The prepared materials have been characterized by X-ray diffraction (XRD) and TEM. The crystallite sizes of all prepared samples are in the range of 50–80 nm applying Scherer’s formula. The electrical studies and fuel cell performance have been completed at temperature ≤ 700 °C. The doping of boron into ceria has significantly improved the electrical conduction of pure ceria oxide which has been studied using four-probe setup. The maximum ionic conductivity and power density of B 0.20 :Ce 0.80 (molar ratio) electrolyte material named as E4 have been achieved and found to be 0.09 S/cm at 700 °C and 198.125 mW/cm 2 at 650 °C. It has been observed that all electrochemical results are consistent with the doping of boron into ceria.

The Pt–Fe 2 O 3 nanoparticles embedded over N, P-doped carbon (Pt–Fe 2 O 3 /NPC) was successfully synthesized by chemical reduction method demonstrating an enhanced electrocatalytic efficacy in alkaline media toward oxygen reduction reaction (ORR). The surface morphology of Pt–Fe 2 O 3 /NPC has been characterized by electron microscopy scanning, X-ray diffraction, electron microscopy transmission, Raman spectra, and X-ray photoelectron spectroscopy. The ORR electrocatalytic activity of Pt–Fe 2 O 3 /NPC was found to be the superior mass activity of 0.120 mA µg −1 , which are almost twice higher than those for Pt–Fe 2 O 3 /VC (0.068 mA µg −1 ) and Pt/C (0.061 mA µg −1 ) catalysts. The durability tests revealed that the Pt–Fe 2 O 3 /NPC exhibited enhanced stability observed from the order of electrochemical active surface area (ECA) loss determined as Pt–Fe 2 O 3 /NPC (45.67%) <Pt–Fe 2 O 3 /VC (62.5%) <(Pt/C (72.13%) after 5000 cycles. This present investigation unveiled a facile approach to develop the number of active sites with the combination between P–Fe 2 O 3 and N, P-doped carbon for improved electrocatalytic performance toward ORR.

Porous buffer layers for anode-supported solid oxide fuel cells (SOFCs) have been investigated for many years with different thicknesses of the buffer layer in each study. In this work, micro-tubular SOFCs having samarium-doped ceria (SDC) and gadolinium-doped ceria (GDC) buffer layers are compared using the current–voltage technique, electrochemical impedance spectroscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The thickness of the porous SDC and GDC buffer layer is investigated systematically with the thickness varying between 0.3 and 2.0 μm. The power density varies between 212 and 1004 mW/cm 2 for samples having different SDC buffer layer thickness. Comparable changes occur for the SOFCs with a GDC buffer layer, but less variation in polarization losses resulted. Variation in electrochemical performance varies due to changes in ohmic resistance, cathode activation polarization, and interfacial reactions between the cathode and electrolyte materials.

In the present study, the catalytic activity of copper-loaded cobalt-based metal–organic framework (ZIF-67) composites was studied for their electrochemical oxygen reduction reaction (ORR). The Cu-ZIF-67 composite was prepared by the solvothermal method. After pyrolysis under argon atmosphere at 700 °C, the composite was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and Fourier transform infrared spectroscopy (FTIR). The electrochemical activity of the composites was tested for ORR in 0.1 M alkaline media using the three-electrode system by cyclic voltammetry (CV), Tafel plots, and electrochemical impedance spectroscopy (EIS). The composites showed variable activity with a current density of 1.32 mA cm −2 at 0.71 V (versus reversible hydrogen electrode (RHE)) onset potential for 70 wt% Cu-ZIF-67, 7.5 mA cm −2 at 0.82 V (versus RHE) onset potential for 50 wt% Cu-ZIF-67, and 11.85 mA cm −2 at 0.85 V (versus RHE) for 30% Cu-ZIF-67. The increasing ratio of the ZIF-67 effect can be attributed to the increased activity of ZIF-67 with the synergistic effect of Cu toward increased current density.

Monodispersed Pt nanoparticles supported on a TiO 2 and nitrogen-doped carbon composite (TiO 2 /NDC) were successfully synthesized via an efficient in situ self-assembly strategy and microwave-assisted polyol process. The Pt/TiO 2 /NDC catalyst exhibited superior electrocatalytic activity toward the methanol oxidation reaction (MOR). The electrochemically active surface area of the Pt/TiO 2 /NDC catalyst was twofold higher than that of the Pt/C/NDC catalyst. In addition, the Pt/TiO 2 /NDC catalyst revealed a better electrocatalytic activity and CO-tolerance as well as a stability toward the MOR. The combined characterization from Fourier transform infrared spectrum, Brunauer-Emmett-Teller surface area, scanning electron microscopy, transmission electron microscopy, energy dispersive spectrometer, thermogravimetric analysis, inductively coupled plasma atomic emissions spectrometry, X-ray diffraction, and X-ray photoelectron spectroscopy analyses demonstrated that the superior catalytic performance and stability of the Pt/TiO 2 /NDC catalysts likely arose from the synergistic effect of their unique morphology and composition as well as the electronic effect between the TiO 2 /NDC and Pt. This electrocatalyst holds great promise for application in direct methanol fuel cells.

Precise porosity control is highly desirable for improving the electrochemical performance of solid oxide fuel cells (SOFCs). Freeze casting is an established method for enabling high bulk porosity in structures and controlling pore orientation. In this study, freeze casting was used to fabricate tubular, anode-supported SOFCs with aligned and varying amounts of porosity by controlling the solids/water ratio in different casting slurries. SOFCs were prepared with a Ni/yttria and scandia stabilized zirconia (ScYSZ) anode support (AS), an anode functional layer (AFL), a ScYSZ electrolyte, a lanthanum strontium manganite (LSM)/ScYSZ cathode interlayer (CIL), and an LSM cathode. The permeability of the anode support was found to increase from 1.4 × 10 −2 to 1.8 × 10 −2 m 2 as porosity was increased from 57 to 64 vol%, while the total cell resistance decreased by 35% from 0.93 to 0.60 Ohm cm 2 . When evaluated with 30 vol% H 2 as the fuel at 800 °C, the decrease of concentration polarization enabled an increase in electrochemical performance by 42% from 0.35 to 0.50 W/cm 2 as the porosity in the anode support was increased. Mechanical strength characterization using a three-point method showed there is a practical upper limit of the amount of porosity that can be designed into the anode support. This work paves a way for controlling porosity by freeze casting and understanding the correlation between porosity and concentration polarization losses in SOFCs.

In this study, two solid oxide fuel cell (SOFC) hybrid systems (anode-supported model (ASM) and electrolyte-supported model (ESM)) is developed in matlab ® and compared. The hybrid system model is considered to investigate the impacts of various operating parameters such as SOFC operating temperature and steam/carbon ratio on power production and performance of the hybrid system where it is projected that results can be utilized as guidelines for optimal hybrid system operation. According to the findings, a maximum 695 kW power is produced at 750 °C operating temperature for the anode-supported model, whereas 627 kW power is produced at 1000 °C for the electrolyte-supported model. The highest electrical efficiencies for the anode-supported model and the electrolyte-supported model are 64.6% and 58.3%, respectively. Besides, the lower value of the steam to carbon ratio is favorable for increased power output from the fuel cell and consequently a high SOFC efficiency.

Presented here is a novel system that uses an aluminum-based fuel to continuously produce electrical power at the kilowatt scale via a hydrogen fuel cell. This fuel has an energy density of 23.3 kW h/L and can be produced from abundant scrap aluminum via a minimal surface treatment of gallium and indium. These additional metals, which in total comprise 2.5% of the fuel’s mass, permeate the grain boundary network of the aluminum to disrupt its oxide layer, thereby enabling the fuel to react exothermically with water to produce hydrogen gas and aluminum oxyhydroxide (AlOOH), an inert and valuable byproduct. To generate electrical power using this fuel, the aluminum–water reaction is controlled via water input to a reaction vessel in order to produce a constant flow of hydrogen, which is then consumed in a fuel cell to produce electricity. As validation of this power system architecture, we present the design and implementation of two proton-exchange membrane (PEM) fuel cell systems that successfully demonstrate this approach. The first is a 3 kW emergency power supply, and the second is a 10 kW power system integrated into a BMW i3 electric vehicle.

Microstructural changes in Ni–yttria stabilized zirconia (YSZ) near the YSZ electrolyte were examined by three-dimensional (3D) electron microscopy after electrolysis and fuel cell operation up to 10,700 h and 15,000 h, respectively. The depletion of Ni and three-phase boundaries (TPBs) close to the electrolyte was detected upon cathodic polarization. It corresponded to spatial variations of dihedral angles (θ) at TPBs and Ni surface curvature along the direction perpendicular to the electrolyte, which comport with electrowetting and Zener pinning theory on several aspects. θ Ni decreased by up to 6 deg next to the electrolyte after electrolysis but remained uniform after fuel cell operation. This is in line with predictions from electrowetting theory with capacitances measured by electrochemical impedance spectroscopy and distribution of relaxation times. The decrease in θ Ni was concurrent to transition toward concave Ni/pore interfacial shapes and lower genus of the Ni phase, which suggests the pinch-off of Ni ligaments following surface diffusion-controlled Rayleigh instability. The increase in absolute mean curvature near the electrolyte interface is a driving force for outward transport of Ni. The decrease in θ YSZ further suggests that TPB lines relocate on YSZ surface features that provide higher Zener pinning force. In contrast, few localized contact losses between Ni and YSZ that can also occur under high cathodic polarization and trigger Ni depletion were detected. The results are expected to advance the understanding of the driving forces that cause Ni depletion near the electrolyte in electrolysis for the design of improved solid oxide cell electrode microstructures.

This review outlines the approaches and mechanisms through which peptides and amino acids functionalize electrocatalytically active surfaces to promote or inhibit the electrochemical hydrogen evolution reaction (HER). HER is important in many electrochemical systems. For example, HER is highly desired in water electrolysis, which if driven by renewable energy could serve as a green alternative to the fossil-fuel-driven steam methane-reforming process. However, HER is often an undesired side reaction and thus limits the selectivity of promising electrochemical technologies such as electrochemical nitrogen reduction or carbon dioxide reduction. In pursuing higher product selectivity and yield in emerging and existing electrochemical systems, amino acids and short-chain peptides are promising molecules for the modification of electrochemically active surfaces. Peptides are attractive because they are highly tunable, which allows for versatility in their applications. This short review article summarizes literature that illustrates the mechanisms through which electrode-bound peptides can affect HER including via modulating surface binding and adsorbate coverage, altering the surface composition, and controlling proton transfer rates. Our goal is to motivate additional studies utilizing electrode-bound peptides to modulate electrochemical hydrogen evolution reactions.

Voltammetry, potentiometry, amperometry, and electrochemical impedance spectroscopy (EIS) were used to study practical polymer electrolyte membrane fuel cell (PEMFC) stacks in an attempt to validate the stack-tailored electrochemical methods and to show the range of information about a PEMFC stack obtainable with the methods. In-stack electrode voltammetry allowed to determine the type, i.e., the surface chemistry, of catalysts used to make the stack electrodes and to measure the electrodes’ true active surface areas (EASAs). Stack potentiometry gave the EASAs, too, but only after calibration of the method against voltammetry. The speed of the test is the advantage of the stack potentiometry. An amperometry-based protocol was introduced to measure the hydrogen permeability and electronic shorting of the stack membrane-electrode assemblies. Dependence of the H 2 permeability on H 2 pressure and the stack temperature was shown. EIS in the hydrogen-pump mode was used to study the anode and electrolyte membrane processes under load. Spectra were dominated by humidification effects, which allowed probing the external humidification distribution to the anodes in the stack. Cathode EIS spectra obtained by subtraction of H 2 -H 2 -mode spectra from H 2 -air-mode spectra were modeled and the ohmic, charge-transfer, and oxygen mass-transport contributions to the stack polarization under load were separated. The variability of these contributions across the stack was discussed.

The Dusty Gas model (DGM), despite being arguably the most accurate representation of gas diffusion in electrodes, is not readily adopted in the literature as it entails relatively expensive numerical integration of differential equations for concentration polarization calculations. To address this issue, this article demonstrates an analytical procedure to solve the DGM equations in a fuel cell electrode setting. In the process, it highlights the differences with previous attempts in the literature and improves upon the shortcomings. This paper specifically provides explicit expressions of concentration overpotentials of anode-supported solid oxide fuel cells (SOFCs) for binary and ternary gas systems via the analytical solution of DGM equations in one dimension without considering the viscous effects. The model predictions match very well with the experimental data available in the open literature. This paper also provides a semi-analytical framework for higher-order multicomponent systems. Finally, the effect of the pore-size distribution in the porous electrode on the concentration polarization is thoroughly explored.