An Alkaline Al–H2O2 Semi‐Fuel Cell Based on a Nickel Foam Supported Co3O4 Nanowire Arrays Cathode

The electrode of Co₃O₄ nanowire arrays directly grown on nickel foam is prepared via a facile one‐step method. The electrode is characterised by scanning and transmission electron microscopy and tested as the cathode of an Al–H₂O₂ semi‐fuel cell. We found that Co₃O₄ forms clusters of nanowires with length up to around 15 μm and diameter around 250 nm. The nanowire is composed of interconnected nanoparticles. Effects of H₂O₂ concentrations, catholyte KOH concentration, catholyte flow rate and operation temperature on the cell performance are investigated. The cell exhibited an open circuit voltage of 1.4 V, and peak power densities of 85 and 137 mW cm^–2 at 25 and 65 °C, respectively, while running on 0.4 mol L^–1 H₂O₂ at a flow rate of 80 mL min^–1.     

Three‐Dimensional Reconstruction and Microstructure Modeling of Porosity‐Graded Cathode Using Focused Ion Beam and Homogenization Techniques

In this study, microstructure of a porosity‐graded lanthanum strontium manganite (LSM) cathode of solid oxide fuel cells (SOFCs) has been characterized using focused ion beam (FIB) and scanning electron microscopy (SEM) combined with image processing. Two‐point correlation functions of the two‐dimensional (2D) images taken along the direction of porosity gradient are used to reconstruct a three‐dimensional (3D) microstructure. The effective elastic modulus of the two‐phase porosity‐graded cathode is predicted using strong contrast (SC) and composite inclusion (CI) homogenization techniques. The effectiveness of the two methods in predicting the effective elastic properties of the porosity‐graded LSM cathode is investigated in comparison with the results obtained from the finite element model (FEM).     

Preparation and Electrochemical Properties of Sr‐doped K2NiF4‐type Cathode Material Pr1.7Sr0.3CuO4 for IT‐SOFCs

A novel K₂NiF₄‐type oxide Pr_1.7Sr_0.3CuO₄ (PSCu) is studied to obtain its electrochemical properties as the cathode for intermediate‐temperature solid oxide fuel cells (IT‐SOFCs). The PSCu cathode powder and Ce_0.8Sm_0.2O_1.9 (SDC) electrolyte powder were synthesized by sol‐gel method and glycine‐nitrate method, respectively. The crystal structure of PSCu powder and PSCu‐SDC composite powder were identified with X‐ray diffraction (XRD). It is shown that PSCu belongs to tetragonal K₂NiF₄‐type and has good chemical compatibility with SDC. The thermal expansion coefficient (TEC) of PSCu is close to that of SDC. The conductivity of PSCu tested with four‐probe method exhibits a semiconductor‐pseudometal transformation at 400–450 °C, where the maximum conductivity of 103.6 S cm⁻¹ is obtained. The polarization test indicates the area specific resistance (ASR) of PSCu decreases with increasing temperature, reaching 0.11 Ω cm² at 800 °C. The activation energy of oxygen reduction reaction during 600–800 °C is 1.19 eV. The single fuel cell performance test reveals the open circuit voltage (OCV) and resistivity of PSCu reduce with increasing temperature, but the power density ascends with increasing temperature. The maximal power density is 243 mW cm⁻² at 800 °C, and the corresponding current density and OCV are 633 mA cm⁻² and 0.77 V, respectively.     

Synthesis and Electrochemical Properties of BaFe1−xCuxO3−δ Perovskite Oxide for IT‐SOFC Cathode

A series of iron‐based perovskite oxides BaFe_1−xCu_xO_3−δ (x = 0.10, 0.15, 0.20 and 0.25, abbreviated as BFC‐10, BFC‐15, BFC‐20 and BFC‐25, respectively) as cathode materials have been prepared via a combined EDTA‐citrate complexing sol‐gel method. The effects of Cu contents on the crystal structure, chemical stability, electrical conductivity, thermal expansion coefficient (TEC) and electrochemical properties of BFC‐x materials have been studied. All the BFC‐x samples exhibit the cubic phase with a space group Pm3m (221). The electrical conductivity decreases with increasing Cu content. The maximum electrical conductivity is 60.9 ± 0.9 S cm⁻¹ for BFC‐20 at 600 °C. Substitution of Fe by Cu increases the thermal expansion coefficient. The average TEC increases from 20.6 × 10⁻⁶ K⁻¹ for BFC‐10 to 23.7 × 10⁻⁶ K⁻¹ for BFC‐25 at the temperature range of 30–850 °C. Among the samples, BFC‐20 shows the best electrochemical performance. The area specific resistance (ASR) of BFC‐20 on SDC electrolyte is 0.014 Ω cm² at 800 °C. The single fuel cell with the configguration of BFC‐20/SDC/NiO‐SDC delivers the highest power density of 0.57 W cm⁻² at 800 °C. The favorable electrochemical activities can be attributed to the cubic lattice structure and the high oxygen vacancy concentration caused by Cu doping.     

Start‐Up of HT‐PEFC Systems Operating with Diesel and Kerosene for APU Applications

Fuel‐cell‐based auxiliary power units offer power generation with reduced fuel consumption and low emissions. A very promising system is the combination of an autothermal reformer with a high‐temperature polymer electrolyte fuel cell. A fast start‐up procedure is a crucial requirement for the use of this system as an auxiliary power unit. This paper reports on the development of a suitable start‐up strategy for a 10 kW_el auxiliary power unit with a start‐up burner. A commercially available diesel burner was tested as a start‐up device. A dynamic MATLAB/Simulink model was developed to analyze different start‐up strategies. With the currently available apparatus and start‐up burner it takes 2,260 s before power generation can begin according to simulation results. The fuel processor alone would be ready for operation after 1,000 s. An optimization of the fuel cell stack with regard to its thermal mass would lead to a start‐up time of 720 s. A reduction to 600 s is possible with a slight customization of the start‐up burner.     

Theoretical Model for the Optimal Design of Air Cooling Systems of Polymer Electrolyte Fuel Cells. Application to a High‐Temperature PEMFC

The cooling system of a high‐temperature PEM fuel cell with a nominal electric power of 1.5 kW for a combined heat and power unit (CHP) has been designed using a thermochemical model. The 1D model has been developed as a simple, predictive, and useful tool to evaluate, design, and optimize cooling systems of PEM fuel cells. As proved, it can also be used to analyze the influence of different operational and design parameters, such as the number and geometry of the channels, or the air flow rate, on the overall performance of the stack. To validate the model, predicted results have been compared with experimental measurements performed in a commercial 2 kW air‐forced open‐cathode stack. The model has then been applied to calculate the air flow required by the designed prototype stack as a function of the power output, as well as to analyze the influence of the cooling channels configuration (cross‐section geometry and number) on the heat management. Results have been used to select the optimum air‐fan cooling system, which is based on compact axial fans.     

Electrochemical Evaluation of Porous Non‐Platinum Oxygen Reduction Catalysts for Polymer Electrolyte Fuel Cells

A porous non‐platinum electrocatalyst for the oxygen reduction reaction (ORR), obtained by pyrolysing a cobalt porphyrin precursor, was evaluated by electrochemical means. The reactivity of the non‐platinum ORR catalyst was investigated with a rotating disc electrode (RDE) experimental set up. RDE data were collected in an acidic electrolyte containing N₂, O₂, CO and under mixed reactant O₂/methanol conditions. The electrochemical performance of such‐obtained non‐platinum catalyst is discussed and compared to platinum‐based ORR catalysts. Based on the results collected here, we are able to propose and test possible proton exchange fuel cell (PEFC) operating conditions where non‐platinum ORR catalysts can be utilised. Direct methanol fuel cell (DMFC) data demonstrating a superior performance of the non‐platinum catalyst relative to platinum black, often perceived as the state‐of‐the‐art oxygen–reduction catalyst for the DMFC cathode is presented.     

Evaluation of Using LaNi0.6Fe0.4O3–δ Contact Layer Between La0.6Sr0.4FeO3 Cathode and Crofer22APU Interconnect for Solid Oxide Fuel Cells

Interconnect‐cathode interfacial adhesion is important for the durability of solid oxide fuel cell (SOFC). Thus, the use of a conductive contact layer between interconnect and cathode could reduce the cell area specific resistance (ASR). The use of La_0.6Sr_0.4FeO₃ (LSF) cathode, LaNi_0.6Fe_0.4O_3–δ (LNF) contact layer and Crofer22APU interconnect was proposed as an alternative cathode side. LNF‐LSF powder mixtures were heated at 800 °C for 1,000 h and at 1,050 °C for 2 h and analyzed by X‐Ray power diffraction (XRD). The results indicated a low reactivity between the materials. The degradation occurring between the components of the half‐cell (LSF/LNF/Crofer22APU) was studied. XRD results indicated the formation of secondary phases, mainly: SrCrO₄, A(B, Cr)O₃ (A = La, Sr; B = Ni, Fe) and SrFe₁₂O₁₉. Scanning electron microscopy with energy dispersive X‐Ray spectroscopy (SEM‐EDX) and the X‐Ray photoelectron spectroscopy (XPS) analyzes confirmed the interaction between LSF/LNF and the metallic interconnect due to the Cr vaporization/migration. An increment of the resistance of ∼0.007 Ω cm² in 1,000 h is observed for (LSF/LNF/Crofer22APU) sample. However, the ASR values of the cell without contact coating, (LSF/Crofer22APU), were higher (0.31(1) Ω cm²) than those of the system with LNF coated interconnect (0.054(7) Ω cm²), which makes the proposed materials combination interesting for SOFC.     

Co‐synthesis of Sm0.5Sr0.5CoO3‐Sm0.2Ce0.8O1.9 Composite Cathode with Enhanced Electrochemical Property for Intermediate Temperature SOFCs

A 70 wt.% Sm_0.5Sr_0.5CoO₃ – 30 wt.% Sm_0.2Ce_0.8O_1.9 (SSC–SDC73) composite cathode was co‐synthesized by a facile one‐step sol–gel method, which showed lower polarization resistance and overpotential than those of physically mixed SSC–SDC73 cathode. The polarization resistance of co‐synthesized SSC–SDC73 cathode at 800 °C was as low as 0.03 Ω cm² in air. Scanning electron microscopy (SEM) images showed that the enhanced electrochemical property was mainly attributed to the smaller grains and good dispersion of SSC and SDC phases within the composite cathode, leading to an increase in three‐phase boundary length. The dependence of polarization resistance with oxygen partial pressure indicated that the rate‐limiting step for oxygen reduction reaction was the dissociation of molecular oxygen to atomic oxygen process. An anode supported fuel cell with a co‐synthesized SSC–SDC73 cathode exhibited a peak power density of 924 mW cm⁻² at 800 °C. Our results suggested that co‐synthesized composite was a promising cathode for intermediate temperature solid oxide fuel cells (IT‐SOFCs).     

Optimization of a High Temperature PEMFC micro‐CHP System by Formulation and Application of a Process Integration Methodology

A 1 kWe micro combined heat and power (CHP) system based on high temperature proton exchange membrane fuel cell (PEMFC) technology is modeled and optimized by formulation and application of a process integration methodology. The system can provide heat and electricity for a single‐family household. It consists of a fuel cell stack, a fuel processing subsystem, heat exchangers, and balance‐of‐plant components. The optimization methodology involves system optimization attempting to maximize the net electrical efficiency, and then by use of a mixed integer nonlinear programming (MINLP) problem formulation, the heat exchange network (HEN) annual cost is minimized. The results show the high potential of the proposed model since high efficiencies are accomplished. The net electrical efficiency and total system efficiency, based on lower heating value (LHV), are 35.2% and 91.1%, respectively. The minimized total annual cost of the HEN is $8,147 year^–1.     

Two‐Phase 1D+1D Model of a DMFC: Development and Validation on Extensive Operating Conditions Range

A two‐phase 1D+1D model of a direct methanol fuel cell (DMFC) is developed, considering overall mass balance, methanol transport in gas phase through anode diffusion layer, methanol and water crossover. The model is quantitatively validated on an extensive range of operating conditions, 24 polarisation curves. The model accurately reproduces DMFC performance in the validation range and, outside this, it is able to predict values under feasible operating conditions. Finally, the estimations of methanol crossover flux are qualitatively and quantitatively similar to experimental measures and the main local quantities' trends are coherent with results obtained with more complex models.     

Improving the Stability and Ethanol Electro‐Oxidation Activity of Pt Catalysts by Selectively Anchoring Pt Particles on Carbon‐Nanotubes‐Supported‐SnO2

To improve the stability and activity of Pt catalysts for ethanol electro‐oxidation, Pt nanoparticles were selectively deposited on carbon‐nanotubes (CNTs)‐supported‐SnO₂ to prepare Pt/SnO₂/CNTs and Pt/CNTs was prepared by impregnation method for reference study. X‐ray diffraction (XRD) was used to confirm the crystalline structures of Pt/SnO₂/CNTs and Pt/CNTs. The stabilities of Pt/SnO₂/CNTs and Pt/CNTs were compared by analyzing the Pt size increase amplitude using transmission electron microscopy (TEM) images recorded before and after cyclic voltammetry (CV) sweeping. The results showed that the Pt size increase amplitude is evidently smaller for Pt/SnO₂/CNTs, indicating the higher stability of Pt/SnO₂/CNTs. Although both catalysts exhibit degradation of electrochemical active surface area (EAS) after CV sweeping, the EAS degradation for the former is lower, further confirming the higher stability of Pt/SnO₂/CNTs. CV and potentiostatic current–time curves were recorded for ethanol electro‐oxidation on both catalysts before and after CV sweeping and the results showed that the mass specific activity of Pt/CNTs increases more than that of Pt/SnO₂/CNTs, indicating that Pt/CNTs experiences more severe evolution and is less stable. The calculated area specific activity of Pt/SnO₂/CNTs is larger than that of Pt/CNTs, indicating SnO₂ can co‐catalyze Pt due to plenty of interfaces between SnO₂ and Pt.     

Residual Stress and Buckling Patterns of Free‐standing Yttria‐stabilized‐zirconia Membranes Fabricated by Pulsed Laser Deposition

The residual stress and buckling patterns of free‐standing 8 mol.% yttria‐stabilized‐zirconia (8YSZ) membranes prepared by pulsed laser deposition and microfabrication techniques on silicon substrates are investigated by wafer curvature, light microscopy, white light interferometry, and nanoindentation. The 300 nm thin 8YSZ membranes (390 μm × 390 μm) deposited at 25 °C are almost flat after free‐etching, whereas deposition at 700 °C yields strongly buckled membranes with a compressive stress of –1,100 ± 150 MPa and an out‐of‐plane‐displacement of 6.5 μm. These latter membranes are mechanically stable during thermal cycling up to 500 °C. Numerical simulations of the buckling shape using the Rayleigh–Ritz‐method and a Young's modulus of 200 GPa are in good agreement with the experimental data. The simulated buckling patterns are used to extract the local stress distribution within the free‐standing membrane which consists of tensile and compressive stress regions that are below the failure stresses. This is important regarding the application in, e.g., microsolid oxide fuel cell membranes which must be thermomechanically stable during microfabrication and device operation.     

Performance Study of Direct Borohydride Fuel Cells Employing Polyvinyl Alcohol Hydrogel Membrane and Nickel‐Based Anode

A direct borohydride fuel cell (DBFC) employing a polyvinyl alcohol (PVA) hydrogel membrane and a nickel‐based composite anode is reported. Carbon‐supported platinum and sputtered gold have been employed as cathode catalysts. Oxygen, air and acidified hydrogen peroxide have been used as oxidants in the DBFC. Performance of the PVA hydrogel membrane‐based DBFC was tested at different temperatures and compared with similar DBFCs employing Nafion® membrane electrolytes under identical conditions. The borohydride–oxygen fuel cell employing PVA hydrogel membrane yielded a maximum peak power density of 242 mW cm^–2 at 60 °C. The peak power densities of the PVA hydrogel membrane‐based DBFCs were comparable or a little higher than those using Nafion® 212 membranes at 60 °C. The fuel efficiency of borohydride–oxygen fuel cell based on PVA hydrogel membrane and Ni‐based composite anode was found to be between 32 and 41%. The cell was operated for more than 100 h and its performance stability was recorded.     

Solid‐State Structure and Mechanical Properties of Blends of an Amorphous Polyamide and a Poly(amino‐ether) Resin

Summary: Finely dispersed blends of an amorphous polyamide (AP) and a poly(amino‐ether) (PAE) resin were obtained by direct injection moulding. The blend components reacted slightly, mainly in PAE‐rich compositions, as seen by torque increases and FT‐IR. Both negative volumes of mixing and preferential orientation were observed in blends with very high AP contents, leading to synergisms in both the modulus of elasticity and the yield stress. In PAE‐rich blends, the effects of these two structural characteristics were negative, but the higher presence of reacted products also led to an overall synergistic modulus of elasticity. With the exception of blends very rich in PAE, in which the more extensive reactions led to brittle materials, the reactions compatibilized the blends due to the presence of small amounts of reacted copolymers, probably at the interface.

Cryogenically fractured surface of the skin of the AP/PAE 80/20 w/w blend.     

Thermodynamic Analysis of an Integrated SOFC,Solar ORC and Absorption Chiller for Tri‐generation Applications

Thermodynamic performance assessment of an integrated tri‐generation energy system for power, heating and cooling production is conducted through energy and exergy analyses. Sustainability assessment is performed and some parametric studies are undertaken to analyze the impact of system parameters and environmental conditions on the system performance. The tri–generation system consists of (a) an internal reforming tubular type solid oxide fuel cell (IR‐SOFC), which works at ambient pressure and fueled with syngas, (b) a combustor and a air heat exchanger, (c) a heat recovery and steam generation unit (HRSG), (d) a two‐ stage Organic Rankine cycle (ORC) driven by exhaust gases of SOFC, (e) parabolic trough solar collectors (PTSC), and (f) a lithium‐bromide absorption chiller (AC) cycle driven by exhaust gases from SOFC unit. The largest irreversibility occurs at the SOFC unit due to high temperature requirement for reactions. Fuel utilization factor, recirculation ratio, dead state conditions, and solar unit parameters have influential effects on the system efficiencies. Energy and exergy efficiencies of tri‐generation unit become 85.1% and 32.62%, respectively, for optimum SOFC stack and environmental conditions. The overall system energy and exergy efficiencies are 56.25% and 15.44% higher than that of conventional SOFC systems, respectively.     

Numerical and Experimental Verification of the Polymer Electrolyte Fuel Cell Performances Enhanced by Under‐Rib Convection

Understanding the current density distributions in polymer electrolyte fuel cells (PEFCs) is crucial for designing cell components, such as the flow field of bipolar plates. A new serpentine flow field equipped with sub‐channels and by‐passes (SFFSB) was numerically and experimentally confirmed to enhance the reactant transport rates and liquid removal efficiency compared with a conventional advanced serpentine flow field (CASFF). Consequently, the maximum current and the power densities of the SFFSB were increased due to the promotion of under‐rib convection. In this study, current density distributions are measured under transient conditions to verify the PEFC performances enhanced by under‐rib convection. The current density distributions of the SFFSB are compared with those of the CASFF. The results show that the SFFSB has a higher local current density and a more uniform distribution than the CASFF, therefore, the PEFC performances with the new flow field of SFFSB is enhanced by the better current density distributions.     

Fabrication of Aluminum Bipolar Plates by Semi‐solid Forging Process and Performance Test of TiN Coated Aluminum Bipolar Plates

Aluminum bipolar plates that can replace graphite bipolar plates for PEM fuel cells are made by applying a semi‐solid forging process. A semi‐solid slurry is made using electromagnetic stirring (EMS), and the resulting slurry is injected into a forging die attached to a 200 ton hydraulic press. The slurry is then compressed with a punch, flowed into a die cavity, and solidified into the bipolar plate form. A356 (cast Al alloy), A6061 (wrought Al alloy), and A1100 (pure Al) are used to make the plates. Titanium nitride (TiN) coating is deposited on the aluminum bipolar plates. An atomic force microscope (AFM) is used to measure the surface roughness of the plates. TiN coated A356 and A1100 plates have a surface roughness of R_a < 1.2 μm. The plate thickness is 1.2 mm. The active area of the channel is 70 mm × 70 mm, with a depth and width of 0.3 and 1.0 mm, respectively. The three TiN‐coated aluminum plates are combined with a unit cell for a performance test. Our results show that a current density value of 473 mA cm^–2 (about 41% of the current density value of commercial graphite plates) can be obtained.     

Performance Evaluation and Parametric Optimization of a Proton Exchange Membrane Fuel Cell/heat‐driven Heat Pump Hybrid System

With the help of the current models of proton exchange membrane (PEM) fuel cells and three‐heat‐source heat pumps, a generic model of a PEM fuel cell/heat‐driven heat pump hybrid system is established, so that the waste heat produced in the PEM fuel cell may be availably utilized. Based on the theory of electrochemistry and non‐equilibrium thermodynamics, expressions for the efficiency and power output of the PEM fuel cell, the coefficient of performance and rate of pumping heat of the heat‐driven heat pump, and the equivalent efficiency and power output of the hybrid system are derived. The curves of the equivalent efficiency and power output of the hybrid system varying with the electric current density and the equivalent power output versus efficiency curves are represented through numerical calculation. The general performance characteristics of the hybrid system are analyzed. The optimally operating regions of some important parameters of the hybrid system are determined. The influence of some main irreversible losses on the performance of the hybrid system is discussed in detail. The advantages of the hybrid system are revealed.     

Tuning the Performance of Ni‐Based Catalyst by Doping Coinage Metal on Steam Reforming of Methane and Carbon‐Tolerance

Density functional theory (DFT) calculations are employed to investigate the key reactions in steam reforming of methane (SRM) on Ni‐based bimetallic surface alloys, including the dissociation of CH₄ and H₂O, the oxidation of CH by oxygen atom to form formyl (CHO), and the dehydrogenation of CHO to form carbon monoxide (CO). The aim of this investigation is to hunt for an optimal catalyst for SRM, which can inhibit carbon formation while maintaining high activity to the SRM. Coinage metal impurity (Au, Ag, and Cu) doped Ni catalysts have been proven to inhibit carbon deposition. In this work, we focus on investigating the doping effects on some leading processes in SRM. It is found that the coinage metal doping has a little effect on the two‐step dissociation of H₂O, which has a linear correlation between the dissociation barriers and the OH–H coadsorption energies. In addition, the dehydrogenation of CHO is kinetically favorable on all alloy surfaces. However, for the CH oxidation to CHO, only the Ni–Cu surface remains high activity. These results suggest that Ni–Cu bimetallic material is an excellent active carbon‐tolerance SRM catalyst for solid‐oxide fuel cells.