Nanostructured Pt–Fe/C cathode catalysts for direct methanol fuel cell: The effect of catalyst composition

A series of carbon supported Pt–Fe bimetallic nanocatalysts (Pt–Fe/C) with varying Pt:Fe ratio were prepared by a modified ethylene glycol (EG) method, and then heat-treated under H₂–Ar (10 vol%-H₂) atmosphere at 900 °C. The Pt–Fe/C catalysts were characterized by X-ray diffraction (XRD), transmission electron spectroscopy (TEM), energy dispersive analysis by X-rays (EDX) and induced coupled plasma-atomic emission spectroscopy (ICP-AES). XRD analysis shows that Pt–Fe/C catalysts have small crystalline particles and form better Pt–Fe alloy structure with Fe amount increasing. TEM images evidence that small Pt–Fe nanoparticles homogeneously deposited on carbon support and addition of Fe can effectively prevent Pt particles agglomeration. EDX and ICP-AES show that Fe precursor cannot be fully reduced and deposited on carbon support through the adopted EG reduction approach. The electrochemical surface area of Pt–Fe/C catalyst obtained through hydrogen desorption areas in the CV curve increases with Fe atomic percentage increasing from 0 to ca. 50%, and then decreases with more Fe in the Pt–Fe/C catalyst. RDE tests show that the Pt–Fe/C with a Pt:Fe ratio of 1.2:1 and an optimized lattice parameter of around 3.894 Å has the highest mass activity and specific activity to oxygen reduction reaction (ORR). As cathode catalyst, this Pt–Fe/C (Pt:Fe ratio of 1.2:1) exhibits higher direct methanol fuel cell performance at 90 °C than Pt/C and other Pt–Fe/C catalysts, this could be attributed to its smaller particle size and better Pt–Fe alloy structure.     

Highly stable Ti–Co–Phen/C catalyst as the cathode for proton exchange membrane fuel cells

A Ti–Co–Phen/C catalyst was prepared for polymer electrolyte membrane fuel cells (PEMFCs) without precious metals using a modified polymer complex (PC) method with 1,10-phenanthroline (Phen) as the nitrogen precursor. The oxygen reduction reaction (ORR) activity of the Ti–Co–Phen/C catalyst was significantly higher than the ORR activity of the Ti–Co/C catalyst prepared with the PC method because the former had a larger N surface content due to its highly dispersed Co species. The catalyst also exhibited excellent chemical stability in acidic media due to the probable strong interactions between the highly dispersed Ti and Co species. A H₂/O₂ PEMFC using the Ti–Co–Phen/C catalyst as the cathode demonstrated excellent cell performance. A 0.68 W cm⁻² maximum power density was obtained. The cell performance stability did not drop perceptibly during its 550-h lifetime at 0.5 V and its 300-h lifetime at 0.7 V. The prepared Ti–Co–Phen/C catalyst exhibited both high ORR activity and excellent performance stability, making it a promising alternative for the cathode catalysts in PEMFCs.     

Clay as a dispersant in the catalyst layer for zinc–air fuel cells

This study proposes a four-layer membrane electrode assembly (MEA) consisting of air-electrode, proton exchange membrane, Zn-electrode with KOH or NaCl aqueous electrolyte and a steel supporter, for use in Zn–air fuel cells. Montmorillonite clay was used to disperse carbon black (CB) and MnO₂ catalyst to improve the performance of the air-electrode. The microstructures of the air-electrode and cell characteristics were investigated by field emission scanning electron microscopy (FE-SEM), optical microscopy (OM) and an electrochemical analyzer. The experimental results indicate that the four-layer MEA for Zn–air fuel cells reached a power density of 6 mW cm⁻² (at 10 mA cm⁻²) without electrolyte leakage from the cells. The open circuit voltage (OCV) and current density were improved by adding clay to the air-electrode as clay can minimize CB aggregation. In the polarization test, the OCV value (1.40 V) reached approximately 90% of the standard potential (1.65 V) and remained steadily over 48 h. These experimental results demonstrate the four-layer MEA can replace conventional Zn–air fuel cells that utilize aqueous electrolyte.     

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.     

Pd decorated Co–Ni nanowires as a highly efficient catalyst for direct ethanol fuel cells

The storage and conversion of energy necessitates the use of appropriate electrochemical systems and chemical reaction catalysts. This work presents newly developed catalysts for electrooxidation of ethanol in an alkaline medium. Nanocatalysts composed of Co–Ni nanowires (Co–Ni NWs) decorated with Pd nanoparticles (Pd NPs) were made at varying metal ratios and their chemical composition and structure was investigated in detail. The synthesis involved a wet chemical reduction assisted by a magnetic field, which led to the generation of NWs, followed by the deposition of spherical Pd NPs on their surface. The best catalytic activity was obtained for the catalyst made of Co₃–Ni₇ decorated with Pd NPs, which exhibited EOR of 8003 mA/mg_Pd for only 0.86 wt% of Pd loading. The results can be explained by the synergistic effect between the morphology of the bimetallic support and the favorable interaction of oxophilic Co, Ni with catalytic Pd.     

Development of non-noble Co–N–C electrocatalyst for high-temperature proton exchange membrane fuel cells

The development of a non-noble Co–N/MWCNT (MWCNT = multi-walled carbon nanotubes) electrocatalyst is achieved through the high-temperature pyrolysis method and successfully characterized by five-step physico-chemical analysis. By utilizing high-resolution analytical surface characterization methods, the chemical states of elements are determined, and the presence of Co-N_x sites is confirmed. ORR activity of a Co–N/MWCNT is found to be auspicious. The maximum number of transferred-electron (n) and the diffusion-limiting current density (j_d) are calculated as 3.95 and 4.53 mA· cm⁻², respectively. The catalyst is further evaluated under a single-cell test station. The test results show that the current and power density values of Co–N/MWCNT are found superior to those of the commercial Pt/C at the 150 °C and 160 °C (e.g., 57 vs. 69 mW· cm⁻² at 150 °C). Due to some stability issues, it is observed that the performance of the Co–N/MWCNT catalyst is slightly decreased while switching the temperature towards 180 °C.     

Effect of carbon substrate materials as a Pt–Ru catalyst support on the performance of direct methanol fuel cells

The support effect of carbon nanotubes (CNTs) for direct methanol fuel cell (DMFC) was studied using CNTs with and without defect preparation, carbon black, and fishbone-type CNTs. The Pt–Ru/defect-free CNTs afforded the highest catalytic activity of methanol oxidation reaction (MOR) in rotating disk electrode experiments and the highest performance as the anode catalysts in DMFC single cell tests with the one-half platinum loading compared to Pt–Ru/VulcanXC-72R. CO stripping voltammograms with Pt–Ru/defect-free CNTs also revealed the lowest CO oxidation potential among other Pt–Ru catalysts using different carbon support. It is thus considered that the carbon substrates significantly affect the CO oxidation activity of anode electrocatalysts in DMFC. This is ascribed to the geometrical effect that the flat interface between CNTs and metal catalysts has a unique feature, at which the electron transfer occurs, and this interface would modify the catalytic properties of Pt–Ru particles.     

Performance of organic–inorganic hybrid anion-exchange membranes for alkaline direct methanol fuel cells

A series of organic–inorganic membranes were prepared through sol–gel reaction of quaternized poly(vinyl alcohol) (QAPVA) with different contents of tetraethoxysilanes (TEOS) for alkaline direct methanol fuel cells. These hybrid membranes are characterized by FTIR, X-ray diffraction (XRD), scanning electron microscopy/energy-dispersive X-ray analysis (SEM/EDXA) and thermo gravimetric analysis (TGA). The ion exchange content (IEC), water content, methanol permeability and conductivity of the hybrid membranes were measured to evaluate their applicability in fuel cells. It was found that the addition of silica enhanced the thermal stability and reduced the methanol permeability of the hybrid membranes. The hybrid membrane M-5, for which the silica content was 5 wt%, showed the lowest methanol permeability and the highest ion conductivity among the three hybrid membranes. The ratio of conductivity to methanol permeability of the membrane M-5 indicated that it had a high potential for alkaline direct methanol fuel cell applications.     

Tuning morphology and structure of Fe–N–C catalyst for ultra-high oxygen reduction reaction activity

Exploring efficient and durable non-precious metal catalysts for oxygen reduction reaction (ORR) has long been pursued in the field of metal-air batteries, fuel cells, and solar cells. Rational design and controllable synthesis of desirable catalysts are still a great challenge. In this work, a novel approach is developed to tune the morphologies and structures of Fe–N–C catalysts in combination with the dual nitrogen-containing carbon precursors and the gas-foaming agent. The tailored Fe–N₁/N₂–C-A catalyst presents gauze-like porous nanosheets with uniformly dispersed tiny nanoparticles. Such architectures exhibit abundant Fe-N_x active sites and high-exposure surfaces. The Fe–N₁/N₂–C-A catalyst shows extremely high half-wave potential (E_1/2, 0.916 V vs. RHE) and large limiting current density (6.3 mA cm⁻²), far beyond 20 wt% Pt/C catalyst for ORR. This work provides a facile morphological and structural regulation to increase the number and exposure of Fe-N_x active sites.     

Ultrafine amorphous Co–W–B alloy as the anode catalyst for a direct borohydride fuel cell

The ultrafine amorphous Co–W–B alloy has been synthesized by chemical reduction and used as anode catalyst in direct borohydride fuel cell. The results show that the maximum power output of the cell is 101 mW cm⁻² at 15 °C, and the essential power density of this material can be up to 350 mW cm⁻² at 15 °C and 500 mW cm⁻² at 60 °C, respectively. The cell has also a good durability, with no attenuation observed after one week of operation.     

Numerical investigation of tridirectionally synergetic Nafion® ionomer gradient cathode catalyst layer for polymer electrolyte membrane fuel cells

Pervious studies have compressively examined a single direction ionomer gradient cathode catalyst layer (CCL) for enhancement of polymer electrolyte membrane (PEM) fuel cells. However, a tridirectionally synergetic (TS) ionomer gradient CCL has not been investigated to date. It is reported that the design of multi-directional ionomer gradient CCL is significant for fuel cells. Therefore, this study proposes a novel TS gradient CCL for fuel cells. By implementing a three-dimensional multiphase fuel cell model, the novel TS gradient CCL is evaluated regarding internal physicochemical quantity distributions and overall cell performance. Numerical results indicate that in comparison with CCL with uniform and a single direction through-plane (TP) or in-plane (IP) ionomer gradient CCL with an identical ionomer content, the novel TS gradient CCL can enhance oxygen diffusion and proton conductivity within porous electrodes, thus improving the maximum power density by approximately 6.8%. Moreover, the optimal TS ionomer gradient CCL contributes to a reduction in coefficient variation of current density within CCL by 10.3% and 17.1% compared to that of uniform and TP(X) gradient CCLs, leading to more homogeneous internal physical quantity profiles, ultimately benefiting the stable operation and durability of fuel cells. The findings here can provide a new insight for guiding the design of ionomer gradient CCL.     

Performance of supported Au–Co alloy as the anode catalyst of direct borohydride-hydrogen peroxide fuel cell

Au–Co alloys supported on Vulcan XC-72R carbon were prepared by the reverse microemulsion method and used as the anode electrocatalyst for direct borohydride-hydrogen peroxide fuel cell (DBHFC). The physical and electrochemical properties were investigated by energy dispersive X-ray (EDX), X-ray diffraction (XRD), cyclic voltammetry, chronamperometry and chronopotentiometry. The results show that supported Au–Co alloys catalysts have higher catalytic activity for the direct oxidation of BH₄⁻ than pure nanosized Au catalyst, especially the Au₄₅Co₅₅/C catalyst presents the highest catalytic activity among all as-prepared Au–Co alloys, and the DBHFC using the Au₄₅Co₅₅/C as anode electrocatalyst shows as high as 66.5 mW cm⁻² power density at a discharge current density of 85 mA cm⁻² at 25 °C.     

Insight towards kinetics and stability of carbon supported Pd–Y2O3 as cathode catalyst for polymer electrolyte fuel cells

Pd–Y₂O₃ on carbon (Pd–Y₂O₃/C) in different mass ratios of Pd to Y₂O₃ (1:1, 2:1, 3:1) were prepared and subjected as cathode electrocatalyst for polymer electrolyte fuel cells (PEFC). X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used to determine the structure, crystalline size and dispersion of Pd–Y₂O₃/C respectively. The electrochemical characterizations of the electrocatalysts were evaluated from Cyclic Voltammetry (CV) and Linear Sweep Voltammetry (LSV). These electrocatalysts were evaluated for their catalytic activity towards oxygen reduction reaction (ORR) in fuel cell. Pd₂–Y₂O₃/C catalyst shows higher power density of 325 mW cm^?2 than Pd₁–Y₂O₃/C, Pd₃–Y₂O₃/C and Pd/C.     

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.     

Investigation of a carbon-supported quaternary PtRuSnW catalyst for direct methanol fuel cells

An investigation was carried out in the electro-oxidation of methanol on a carbon-supported quaternary PtRuSnW catalyst prepared by a liquid-phase reduction method. As derived by X-ray diffraction and X-ray photoelectron spectroscopy, the catalyst was composed of metallic Pt, microcrystalline RuO₂ and SnO₂ phases and amorphous WO₃/WO₂ species. The electrochemical analysis was carried out in half-cell containing sulfuric acid electrolyte as well as in a liquid methanol-fed solid polymer electrolyte single-cell. The activity of catalyst in the half-cell varied as a function of the methanol concentration, it increased with CH₃OH molarity in the activation-controlled region and showed a maximum in 2 M CH₃OH at high currents. IR-free polarization curves showed that the activity of the quaternary catalyst was superior to Pt metal/C samples having the same Pt amount. The presence of semi-insulating metal oxides such as RuO₂, SnO₂ and WO₃ on the electrode surface exhibited a significant uncompensated resistance. The single-cell performance was lower than that predicted by the half-cell experiments mainly due to the methanol cross-over through the Nafion membrane.     

The optimization of electrolyte flow management to increase the performance of Zn–air fuel cells

Zinc (Zn)–air fuel cells (ZAFCs) are one of the potential alternatives to fossil fuels. Because a flowing electrolyte can directly affect cell performance, we focused on the electrolyte management of a ZAFC. The ZAFC galvanostatic discharge was examined to determine its performance. The electrolyte concentration, temperature, and circulation rate were used as the operating parameters for discharge tests, and the relationship between electrolyte and cell performance was discussed based on the experimental results. To elucidate the effect of electrolyte-flow, the computation fluid dynamic simulations have been first performed. The results revealed that the cell performance associating the remnant oxygen in the electrolyte channel     

Performance studies of Pd–Pt and Pt–Pd–Au catalyst for electro-oxidation of glucose in direct glucose fuel cell

Platinum is employed as anode catalyst for low temperature electro-oxidation of glucose in direct glucose fuel cell (DGFC), but it suffers from poisoning by intermediate oxidation products. In the present investigation, palladium and gold precursors are added with platinum precursor to form low metal loading (∼15–20% by wt.) carbon supported catalyst by NaBH₄ reduction technique. The prepared PtPdAu/C (metal ratio 1:1:1) and PdPt/C (metal ratio 4:1) catalysts are tested in DGFC. The Physical characterization of electro-catalysts by scanning electron microscope, transmission electron microscope, energy dispersive X-ray, X-ray diffraction and thermo-gravimetric analysis confirms the formation of nano-sized metal particles on carbon substrate with two prominent homogeneous bi- or tri-metallic crystal phases for PtPdAu/C. The cyclic voltammetry studies carried out for glucose (0.05 M) oxidation in (0.5 M KOH) alkaline medium shows the metal catalysts can efficiently electro-oxidize glucose. The catalysts tested as anode in a batch type DGFC using commercial activated charcoal as cathode produced peak power density of 0.52 mW cm⁻² for both PdPt/C and PtPdAu/C in 0.3 M glucose in 1 M KOH solution.     

Facile synthesis of supported Pt–Cu nanoparticles with surface enriched Pt as highly active cathode catalyst for proton exchange membrane fuel cells

Carbon supported Pt–Cu catalyst (PtCu/C) with surface enriched Pt was synthesized by annealing the Pt-deposited Cu particles. X-ray diffraction (XRD) results indicate the formation of disordered Pt–Cu alloy phase with a high level of Cu/Pt atomic ratio. X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma (ICP) analysis confirm the surface enrichment of Pt. Electrochemical measurements show that PtCu/C has 3.7 times higher Pt mass activity toward the oxygen reduction reaction (ORR) than commercial Pt/C. The enhanced ORR activity of PtCu/C is attributed to the modified electronic properties of surface Pt atoms, which reduces the surface blocking of the ORR oxygenated species.     

Combinatorial investigation of Pt–Ru–Sn alloys as an anode electrocatalysts for direct alcohol fuel cells

Low-temperature direct alcohol fuel cells fed with different kinds of alcohol (methanol, ethanol and 2-propanol) have been investigated by employing ternary electrocatalysts (Pt–Ru–Sn) as anode catalysts. Combinatorial chemistry has been applied to screen the 66-PtRuSn-anode arrays at the same time to reduce cost, time, and effort when we select the optimum composition of electrocatalysts for DAFCs (Direct Alcohol Fuel Cells). PtRuSn (80:20:0) showed the lowest onset potential for methanol electro-oxidation, PtRuSn (50:0:50) for ethanol, and PtRuSn (20:70:10) for 2-propanol in CV results respectively, and single cell performance test indicated that Ru is more suitable for direct methanol fuel cell system, Sn for direct ethanol fuel cell system, and 2-propanol could be applied as fuel with low platinum composition anode electrocatalyst. The single cell performance results and electrochemical results (CV) were well matched with the combinatorial electrochemical results. As a result, we could verify the availability of combinatorial chemistry by comparing the results of each extreme electrocatalysts compositions as follows: PtRuSn (80:20:0) for methanol, PtRuSn (50:0:50) for ethanol and PtRuSn (20:70:10) for 2-propanol.     

Carbon-supported Pd–Ir catalyst as anodic catalyst in direct formic acid fuel cell

It was reported for the first time that the electrocatalytic activity of the Carbon-supported Pd–Ir (Pd–Ir/C) catalyst with the suitable atomic ratio of Pd and Ir for the oxidation of formic acid in the direct formic acid fuel cell (DFAFC) is better than that of the Carbon-supported Pd (Pd/C) catalyst, although Ir has no electrocatalytic activity for the oxidation of formic acid. The potential of the anodic peak of formic acid at the Pd–Ir/C catalyst electrode with the atomic ratio of Pd and Ir = 5:1 is 50 mV more negative than that and the peak current density is 13% higher than that at the Pd/C catalyst electrode. This is attributed to that Ir can promote the oxidation of formic acid at Pd through the direct pathway because Ir can decrease the adsorption strength of CO on Pd. However, when the content of Ir in the Pd–Ir/C catalyst is too high the electrocatalytic activity of the Pd–Ir/C catalyst would be decreased because Ir has no electrocatalytic activity for the oxidation of formic acid.