Design of efficient bimetallic Pt–Au nanoparticle-based anodes for direct formic acid fuel cells

Formic acid (FA) electro-oxidation (FAO) was investigated at a binary catalyst composed of Pt (PtNPs) and Au (AuNPs) nanoparticles which were electrodeposited simultaneously onto a glassy carbon (GC) substrate. The catalytic activity of the binary modified catalyst toward FAO was significantly influenced by the relative molar ratio of PtNPs and AuNPs. Interestingly, the catalyst with a molar ratio (1:1) of PtNPs and AuNPs showed the highest activity toward the favorable pathway of FAO (ca. 26 times increase in the direct peak current concurrently with a ca. 133 mV negative shift in the onset potential). Such enhancement was believed originating from the outstanding improvement of charge transfer during FAO via the desirable “non-poisoning” pathway along with a significant mitigation of CO poisoning at the electrode surface. The diversity of techniques (cyclic voltammetry, chronoamperometry, electrochemical impedance spectroscopy, field-emission scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction) employed in this investigation offered opportunities to assess and interpret the catalyst's activity and stability and to possess a deliberated overview about its morphology, composition and structure.     

Carbon supported platinum–gold alloy catalyst for direct formic acid fuel cells

The Pt–Au nanoparticles with 1:1 atomic ratio supported on carbon powder were prepared by the co-reduction method using N,N-dimethylformamide coordinated Pt–Au complex as a precursor. Cyclic voltammetry results demonstrated that the PtAu/C catalyst exhibited a higher activity for the formic acid oxidation reaction than did the commercial Pt/C catalyst, reflected by its lower onset potential and higher peak current. The fuel cell performance test at 60 °C showed that the direct formic acid fuel cell with the PtAu/C catalyst yielded about 35% higher power density than did the cell with the Pt/C catalyst.     

Development of ultra–low highly active and durable hybrid compressive platinum lattice cathode catalysts for polymer electrolyte membrane fuel cells

A highly active and stable catalyst/support system is developed by using a two-step process. In the first step, activated carbon composite support (ACCS) is synthesized that retains its activity after accelerated stress test (AST). A 30% Pt/ACCS catalyst shows no loss of mass activity and power density after 5000 cycles at 1.0–1.5 V while the commercial Pt/C and Pt/290G catalysts show drastic mass activity losses (57.5% and 66.2%, respectively) and power density losses (88.7% and 84.0%, respectively). In the second step, Pt catalyst with a compressive Pt lattice (Pt¹) is synthesized through a USC-developed annealing procedure in which Co atoms previously embedded in the support diffuse into Pt. The 30% Pt¹/ACCS shows high initial power density (rated) of 0.174 g_Pt kW^?1 and high stability of 24 mV loss at 0.8 A cm^?2 with an electrochemical active surface area (ECSA) loss of 42% after 30,000 cycles (0.6–1.0 V). The support stability under 1.0–1.5 V potential cycling shows potential loss of 8 mV at 1.5 A cm^?2 and ECSA loss of 22% after 5000 cycles. Improved stability and activity of Pt*/ACCS catalyst are due to synergistic effect of catalytic activity and stability of ACCS and formation of compressive Pt lattice catalyst.     

Performance and durability of Ni–Co alloy cermet anodes for solid oxide fuel cells

Ni alloys are examined as redox-resistant alternatives to pure Ni for solid oxide fuel cell (SOFC) anodes. Among the various candidate alloys, Ni–Co alloys are selected due to their thermochemical stability in the SOFC anode environment. Ni–Co alloy cermet anodes are prepared by ammonia co-precipitation, and their electrochemical performance and microstructure are evaluated. Ni–Co alloy anodes exhibit high durability against redox cycling, whilst the current-voltage characteristics are comparable to those of pure Ni cermet anodes. Microstructural observation reveals that cobalt-rich oxide layers on the outer surface of the Ni–Co alloy particles protect against further oxidation within the Ni alloy. In long-term durability tests using highly humidified hydrogen gas, the use of a Ni–Co cermet with Gd-doped CeO₂ suppresses degradation of the power generation performance. It is concluded that Ni–Co alloy cermet anodes are highly attractive for the development of robust SOFCs.     

Preparation of creep-resistant Ni–5 wt.% Al anodes for molten carbonate fuel cells

Ni–5 wt.% Al anodes for molten carbonate fuel cells (MCFCs) are fabricated using relatively cheap elemental powders instead of expensive alloy powders. The tape-cast green sheets are sintered in various atmospheres: reduction, full oxidation–reduction, and partial oxidation–reduction atmospheres. The anode sintered in a reduction atmosphere shows a morphology of a network structure of an NiAl solid solution with its surface covered with thin Al₂O₃ films, and has relatively low creep resistance. On the other hand, the anode sintered in a full oxidation–reduction atmosphere or the one sintered in a partial oxidation–reduction atmosphere has a morphology of small Al₂O₃ particles dispersed in a network structure. In the former, however, a large number of micropores are created during sintering. The latter does not have the micropore problem and generally exhibits high creep resistance. The highest creep resistance is shown by the anode sintered in a partial oxidation–reduction atmosphere with an oxidation time of 2.5 h.     

Development of nickel–iron bimetallic catalytic layer for solid oxide fuel cells: Effect of citric acid

In this paper, Ni_0.75Fe_0.25 catalyst layers with different citric acid contents (molar ratio of CA to metal ions ranges from 0.1 to 1.5) were prepared using thermal decomposition method. Attention was focused on the effect of citric acid on the phase structure, surface energy and coking resistance of Ni_0.75Fe_0.25 catalyst for solid oxide fuel cells (SOFCs). The FeNi₃ phase can be observed in all reduced catalysts, while the grain size of catalysts increases with increasing CA content. The O₂-TPO profiles and Raman spectra reveal that the CA1.5 catalyst has the best coking resistance among all catalysts. In addition, the cell with the CA1.5 catalyst layer has a maximum peak power density 271 mW cm⁻², when operating at 650 °C in methane. Moreover, the voltage of cell with the CA1.5 catalyst layer still remains 74% of the initial value, after operating in methane for 9 h under a current density of 600 mA cm⁻² at 650 °C, which is much more stable than that of the CA-free catalyst layer (53%).     

Catalytic modification of Ni–Sm-doped ceria anodes with copper for direct utilization of dry methane in low-temperature solid oxide fuel cells

A Cu/Ni/Sm-doped ceria (SDC) anode has been designed for direct utilization of dry methane in low-temperature anode-supported solid oxide fuel cells. The anode is prepared by the impregnation method, whereby a small amount of Cu is incorporated into the previously prepared Ni/SDC porous matrix. After reduction, Cu nanoparticles adhere to and are uniformly distributed on the surface of the Ni/SDC matrix. For the resulting Cu/Ni/SDC anode-supported cell, maximum power density of 317 mW cm⁻² is achieved at 600 °C. The power density shows only ∼2% loss after 12-h operation. The results demonstrate that the Cu/Ni/SDC anode effectively suppresses carbon deposition by decreasing the Ni surface area available and the level of carbon monoxide disproportionation. This combination of effects results in very low-power density loss over the operating time.     

Ultrathin sputtered platinum–gadolinium doped ceria cathodic interlayer for enhanced performance of low temperature solid oxide fuel cells

Improvement of the sluggish oxygen reduction reaction (ORR) is the key to lower the operating temperature of conventional solid oxide fuel cells (SOFCs). Developing a novel nanostructure in the cathodic catalyst layer is one of the efficient ways to reduce the operating temperature while improving fuel cell performance. In this paper, all components of low-temperature SOFCs were prepared on a nanoporous substrate by the sputtering method. For the performance enhancement at low temperature, an ultrathin Pt-Gadolinium Doped Ceria (GDC) cermet interlayer was deposited on the cathode side of electrolyte and demonstrated. A significant improvement in electrochemical performance was observed in the Pt-GDC interlayer fuel cell compared to a reference cell. The peak power density of Pt-GDC cathodic cermet interlayer cell was 334 mW/cm² at 500 °C, which was 42.7% higher than that of the reference cell. Through additional analysis, we confirmed that the observed performance enhancement was attributed to the ultrathin cathodic cermet interlayer, which increases the triple phase boundary and enhances the reaction kinetics for ORR.     

Electrochemical performance and redox stability of solid oxide fuel cells supported on dual-layered anodes of Ni-YSZ cermet and Ni–Fe alloy

A Ni–Fe alloy layer in combination with a cermet layer composed of Ni and yttria-stabilized zirconia (YSZ) cermet layer was explored as an anode for solid oxide fuel cells (SOFCs). The cell supported on the dual-layered anode with straight pore paths showed a maximum power density of 1070 mW cm^?2 at 800 °C, while 737 mW cm^?2 for the one supported on the anode with tortuous pore paths. Electrochemical impedance measurement and distribution of relaxation time analysis revealed that the straight pore paths allowed fast gas phase transport thus mitigating the concentration polarization, and improved the accessibility of electrochemical reaction sites hence reducing the activation polarization. The cell supported on the Ni-YSZ/Ni–Fe dual-layered anode remained intact after 8 redox cycles, whereas the cell supported on the Ni-YSZ single layered anode failed after one redox cycle. It is concluded that the Ni-YSZ/Ni–Fe dual-layered composite explored in the present study is suitable for use as the supporting anode for SOFCs.     

A “special” anhydrous system for the preparation of alloyed Pd1Ce0.5 nanonetworks catalyst supported on carbon nanotubes with high electrochemical oxidation activity for formic acid

Herein, Pd₁Ce_0.5 alloy nanonetworks (ANNs) on multi-walled carbon nanotubes (MWCNTs) supported bimetallic catalyst (referred to Pd₁Ce_0.5/MWCNTs-D) was prepared in deep eutectic solvents (DESs). The Pd₁Ce_0.5/MWCNTs-D catalyst shows remarkable catalytic performance toward formic acid oxidation (FAO) (1968.5 mA mg_Pd^?1) and better CO anti-poisoning capability compare with Pd/MWCNTs-D, Pd/MWCNTs-W (prepared in water) and commercial Pd/C catalysts. The excellent network structure and synergistic effect are the main reasons for the improvement of electrochemical activity of Pd₁Ce_0.5/MWCNTs-D catalyst. This study provides a new method for preparation of high performance Pd-based electrocatalysts for direct formic acid fuel cell (DFAFC) applications.     

Synthesis of ultrafine low loading Pd–Cu alloy catalysts supported on graphene with excellent electrocatalytic performance for formic acid oxidation

Here, surfactant free composite catalysts (Pd–Cu/rGO) with Pd–Cu alloy nanoparticles uniformly distributed on graphene sheets are successfully prepared via a facile hydrothermal approach. Compared with pure Pd/rGO catalyst, the introduction of copper could dramatically enhance the performance of the catalyst in the electrocatalytic formic acid oxidation (FAO) due to the strain effect and the ligand effect. With the optimized atomic ratio of 3:1 between palladium and copper, the alloy nanoparticle shows the smallest size of 2.12 nm, thus endowing the composite catalyst with highest catalytic efficiency. With Pd load as low as 14.5%, a maximum mass current density of 1580 mA mg_Pd⁻¹, and residual current of 69.93 mA mg_Pd⁻¹ at 3000 s was achieved with our Pd₃Cu₁/rGO catalyst in the electrocatalytic FAO process.     

Synergistic catalysis of Pd–Ni(OH)2 hybrid anchored on porous carbon for hydrogen evolution from the dehydrogenation of formic acid

The development of a facile yet efficient strategy to boost the catalytic performance of supported Pd nanoparticles (NPs) toward the dehydrogenation of formic acid (FA) is essential but remains challenging. Here, a novel hybrid nanocatalyst comprising Pd and Ni(OH)₂ supported on porous carbon (PC) is developed. The obtained Pd–Ni(OH)₂/PC nanocatalyst exhibits an excellent catalytic performance for FA dehydrogenation to produce hydrogen. The introduction of Ni(OH)₂ in PC support can significantly promote the catalytic activity of Pd NPs toward FA dehydrogenation. Additionally, the catalytic property of Pd–Ni(OH)₂/PC is correlated with the Pd/Ni ratio. The ₂Pd–₁Ni(OH)₂/PC with the optimum Pd/Ni ratio of 2/1 exhibits the maximum turnover frequency (TOF) of 3409 h⁻¹ at 60 °C for FA dehydrogenation. The highly dispersed ultrafine Pd–Ni(OH)₂ hybrid NPs with numerous accessible active sites and Ni(OH)₂−induced positive synergetic effects with Pd NPs considerably boost the catalytic performance for FA dehydrogenation.     

Contact resistance characteristics of coated metallic bipolar plates for PEM fuel cells – investigations on the effect of manufacturing

The main purpose of this study is to understand the interfacial contact resistance (ICR) characteristics of coated metallic bipolar plates (BPP) manufactured through stamping and hydroforming. To this goal, 51 μm thick SS316L stainless steel sheet blanks were formed into BPPs using two forming techniques (stamping and hydroforming); then these formed plates were coated with three different PVD coatings (CrN, TiN, ZrN) at three different coating thicknesses (0.1, 0.5 and 1 μm). Contact resistance of the formed and coated BPP samples were measured before and after they were exposed to the proton exchange membrane fuel cells (PEMFC) operating conditions (i.e., corrosive environment). ICR tests indicated that CrN coating increased the contact resistance of the samples, unexpectedly. TiN samples showed the best performance in terms of low ICR; however, their ICR dramatically increased after short-term exposure to corrosion. ZrN coating, as well, improved conductivity of the SS316L BPP samples and demonstrated similar ICR performance before and after exposure to corrosion.     

The effect of lithium addition on aluminum-reinforced α-LiAlO2 matrices for molten carbonate fuel cells

The effect of lithium hydroxide (LiOH) addition as a lithium source is discussed as a way to prevent Li-ion shortages in aluminum-based α-LiAlO₂ matrices of molten carbonate fuel cells. Our results show that the use of LiOH as a lithium source to prevent a Li-ion shortage caused by a lithiated Al-reaction during the operation of the cell allows for more stable performance and greater durability than when lithium carbonate (Li₂CO₃) is used as the lithium source. The behavior of high-lithium content mixtures is attributed to the presence of reactive aluminum particles, which promote the formation of lithium aluminate (LiAlO₂) phases at 650 °C. The incorporation of low-melting-point lithium and an efficient pathway to the aluminum in a reinforced matrix has improved the in-situ mechanical strength via the lithiated Al-reaction, and they do not lead to any noticeable loss in cell performance, even after 4000 h of operation. From the post-test results, the cell with LiOH stored in the cathode channel shows effective formation of the stable crystalline phase of α-LiAlO₂ and enhancement of the mechanical strength during cell operation.     

Characterization and performance evaluation of Pt–Ru electrocatalysts supported on different carbon materials for direct methanol fuel cells

The paper addresses the effect of the carbon support on the microstructure and performance of Pt–Ru-based anodes for direct methanol fuel cells (DMFC), based on the study of four electrodes with a carbon black functionalized with HNO₃, a mesoporous carbon (CMK-3), a physical mixture of TiO₂ and carbon black and a reference carbon thermally treated in helium atmosphere (HeTT). It is shown that CMK-3 hinders the growth of the electrocatalyst nanoparticles (2.7 nm) and improves their distribution on the support surface, whereas the oxidized surfaces of HNO₃ carbon and TiO₂+carbon lead to larger (4–4.5 nm), agglomerated particles, and the lowest electrochemical active areas (54 and 26 m² g⁻¹, in contrast with 90 m² g⁻¹ for CMK-3), as determined from CO stripping experiments. However, HNO₃ and TiO₂ are characterized by the lowest CO oxidation potential (0.4 V vs. RHE), thus suggesting higher CO tolerance for the se electrodes. Tests in DMFC configuration show that the three modified electrodes have clearly better performance than the reference HeTT. The highest power density attained with electrodes supported on carbon treated with HNO₃ (65 mW cm⁻²/300 mA cm⁻² at 90 °C) and the equally interesting performance of the TiO₂-based electrodes (53 mW cm⁻²/300 mA cm⁻²), is a strong indication of the positive effect of the presence of oxygenated groups on the methanol oxidation reaction. The results are interpreted in order to identify separate microstructural (electrocatalyst particle size, porosity) and compositional (oxygenated surface groups, presence of oxide phase) effects on the electrode performance.     

Proton conducting membranes based on Poly(2,5-benzimidazole) (ABPBI)–Poly(vinylphosphonic acid) blends for fuel cells

Polymer electrolyte membranes (PEM) were fabricated by blending of Poly(2,5-benzimidazole) (ABPBI) and Poly(vinylphosphonic acid) (PVPA) at several stoichiometric ratios with respect to monomer repeating units. The characterization of the membranes were carried out by using Fourier-transform infrared spectroscopy (FT-IR) for inter-polymer interactions, scanning electron microscope (SEM) for surface morphology as well as homogeneity and thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) for thermal properties. Water uptake measurements were made to investigate the swelling character the blends that was changed with PVPA composition. The spectroscopic measurements and water uptake studies suggested the complexation between ABPBI and PVPA that inhibited dopant exclusion up on swelling in excess water. Proton conductivities of the hydrated and anhydrous samples were measured using impedance spectroscopy. Although the proton conductivity of the blends was lower in the anhydrous state such as 1.8 × 10⁻⁶ S/cm at 150 °C for ABPBI:PVPA with (1:2), it increased to 0.004 S/cm for ABPBI:PVPA (1:4) at 20 °C (RH = 50%).     

Effects and properties of various molecular weights of poly(propylene oxide) oligomers/Nafion acid–base blend membranes for direct methanol fuel cells

Various molecular weights of poly(propylene oxide) diamines oligomers/Nafion^® acid–base blend membranes were prepared to improve the performance of Nafion^® membranes in direct methanol fuel cells (DMFCs). The acid–base interactions were studied by Fourier transform infrared spectroscopy (FT-IR) and differential scanning calorimetry (DSC). The performance of the blend membranes was evaluated in terms of methanol permeability, proton conductivity and cell performance. The proton conductivity was slightly reduced by acid–base interaction. The methanol permeability of the blend D2000/Nafion^® was 8.61 × 10⁻⁷ cm² S⁻¹, which was reduced 60% compared to that of pristine Nafion^®. The cell performance of D2000/Nafion^® blend membranes was enhanced significantly compared to pristine Nafion^®. The current densities that were measured with Nafion^® and 3.5 wt% D2000/Nafion^® blend membranes were 62.5 and 103.5 mA cm⁻², respectively, at a potential of 0.2 V. Consequently, the blend poly(propylene oxide) diamines oligomers/Nafion^® membranes critically improved the single-cell performance of DMFC.     

The effect of ceria content in nickel–ceria composite anode catalysts on the discharge performance for solid oxide fuel cells

Optimum ceria content in nickel–ceria composite anode catalyst from the point of discharge performance is discussed. The ohmic loss increased when the ceria content was higher than 30 mol%. Even though the electrical conductivity of the anode decreased with increasing ceria content in the anode catalyst in association with decreasing nickel content, the ohmic loss was kept low until the ceria content was ≤30 mol% because the semiconducting ceria compensated for the decreased current path owing to the decreasing nickel content. The lowest activation loss was observed when the ceria content in the nickel anode catalyst was 30 mol% and the maximum activation loss was obtained for ceria content of 2 mol%. Ceria content in nickel anode influenced microstructure of the anode matrix. When the CeO₂ content was 2 mol%, sintering of anode catalyst was evident and the porosity of anode matrix was almost 57% - highest in this study. Whereas sintering of anode catalyst was not evident and the porosity of anode matrix was 46% when the ceria content in the nickel anode catalyst was 30 mol%. Activation loss was strongly influenced by microstructure of anode matrix, and highest activation loss when the CeO₂ content was 2 mol% was owing to the inappropriate microstructure for electrochemical reaction: sintering of the anode catalyst and excessive porosity of the anode.     

“Model-based” design of thermal management system of a fuel cell “air-independent” propulsion system for underwater shipboard

The thermal management of the fuel cell stack is critical for high-performance long-term operation. A fuel cell system of underwater vessel has a liquid-to-liquid cooling circuits which is composed of two liquid cooling pumps, two three-way valves, and a shell and tube heat exchanger. The liquid-to-liquid cooling technique makes it easier to reject the reaction heat into the surrounding but it is required refined cooling structure and control algorithm. In this study, a model-based design is applied to evaluate the control algorithm. A fuel cell system simulation model is developed and polarization curves and transient response are validated. A proportional integral controller and control strategy is developed and a nominal state feedback controller is also developed. Those control algorithms are evaluated via the dynamic response under step increases of load, and the control performance of the nominal state feedback controller is compared with the conventional controller (PI). The results show that the presented the nominal state feedback control of performs better than the PI control method with less wear and less control effort on the two circuit cooling modules. The proposed the nominal state feedback control can increase the system energy by 23.9%.