Effect of support materials on the performance of direct ethanol fuel cell anode catalyst

Pt–Ru catalysts supported on mesoporous carbon nitride (MCN), multiwall carbon nano tubes (MWCNTs), treated MWCNTs (t-MWCNTS) and Vulcan-XC were prepared using co-impregnation reduction method for the oxidation of ethanol in direct ethanol fuel cell (DEFC) to study the effect of support material. The MCN support was prepared using SBA-15 as template and t-MWCNTs were prepared by refluxing in HNO₃ and H₂SO₄ mixture (1:3) using MWCNTs. XRD shows the formation of Pt–Ru bi-metallic catalyst with size ranges from 7 to 17 nm using different supports. The catalyst and its supports were characterized by physically and electrochemically. Linear sweep voltammetry, cyclic voltammetry and chrono amperometry studies of the above systems reveal that MCN supported Pt–Ru catalyst shows higher electro-catalytic activity towards ethanol oxidation compared to Pt–Ru in treated t-MWCNTs, MWCNts and Vulcan-XC supports. The performance of DEFC based on maximum power density is found to be in the order Pt–Ru/MCN > Pt–Ru/t-MWCNTs > Pt–Ru/MWCNTs > Pt–Ru/Vulcan-XC. The Pt–Ru/MCN shows highest power density of 61.1 mW cm⁻² at 100 °C, 1 bar pressure with catalyst loading of 2 mg cm⁻² using 2 M ethanol feed.     

Ni–Pt/C as anode electrocatalyst for a direct borohydride fuel cell

In this study, a series of Ni–Pt/C and Ni/C catalysts, which were employed as anode catalysts for a direct borohydride fuel cell (DBFC), were prepared and investigated by XRD, TEM, cyclic voltammetry, chronopotentiometry and fuel cell test. The particle size of Ni₃₇–Pt₃/C (mass ratio, Ni:Pt = 37:3) catalyst was sharply reduced by the addition of ultra low amount of Pt. And the electrochemical measurements showed that the electro-catalytic activity and stability of the Ni₃₇–Pt₃/C catalysts were improved compared with Ni/C catalyst. The DBFC employing Ni₃₇–Pt₃/C catalyst on the anode (metal loading, 1 mg cm⁻²) showed a maximum power density of 221.0 mW cm⁻² at 60 °C, while under identical condition the maximum power density was 150.6 mW cm⁻² for Ni/C. Furthermore, the polarization curves and hydrogen evolution behaviors on all the catalysts were investigated on the working conditions of the DBFC.     

Operating characteristics of direct methanol fuel cell using a platinum–ruthenium catalyst supported on porous carbon prepared from mesophase pitch

The characteristics of a platinum–ruthenium catalyst supported on porous carbon (PC) are analysed by X-ray diffraction, scanning electron microscopy, cyclic voltammetry and chemisorption techniques. Single-cell tests are carried out in order to compare the performance of these catalysts as an anode in a direct methanol fuel cell with respect to that of a commercial-grade catalyst. The methanol oxidation rate on a Pt–Ru catalyst supported on PC with a pore size of 20 nm is about 35% higher than that on a commercial E-TEK catalyst. The catalyst (Pt–Ru/K20) in the single-cell test gives a power density of 90 and 126 mW cm⁻² under air and oxygen at 60 °C, respectively. These values are 15–16% higher than those obtained with a commercial E-TEK catalyst.     

Electrochemical impedance studies on carbon supported PtRuNi and PtRu anode catalysts in acid medium for direct methanol fuel cell

The anodic Pt–Ru–Ni/C and the Pt–Ru/C catalysts for potential application in direct methanol fuel cell (DMFC) were prepared by chemical reduction method. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) measurements were carried out by using a glassy carbon working electrode covered with the catalyst powder in a solution of 0.5 mol L⁻¹ CH₃OH and 0.5 mol L⁻¹ H₂SO₄ at 25 °C. EIS information discloses that the methanol electrooxidation on the Pt–Ru–Ni/C catalyst at various potentials shows different impedance behaviors. The mechanism and the rate-determining step of methanol electrooxidation are changed with increasing potential. Its rate-determining steps are the methanol dehydrogenation and the oxidation reaction of adsorbed intermediate CO_ads and OH_ads in low (400–500 mV) and high (600–800 mV) potentials, respectively. The catalytic activity of the Pt–Ru–Ni/C catalyst is higher for methanol electrooxidation than that of the Pt–Ru/C catalyst. Its tolerance performance to CO formed as one of the intermediates of methanol dehydrogenation is also better than that of the Pt–Ru/C catalyst.     

Application of silica as a catalyst support at high concentrations of methanol for direct methanol fuel cells

Various silica particles were adopted as catalyst supports, and silica-supported PtRu catalysts were evaluated as catalysts for the anode of direct methanol fuel cells at methanol concentrations of 1–10 M through single cell tests. Compared to a carbon black supported Pt–Ru catalysts, the silica-supported Pt–Ru catalysts exhibited higher performance in MEA, especially with high concentration over 3 M, and the maximum power density reached to 90 mW cm⁻² and 60 mW cm⁻² with 5 M and 10 M, respectively, which were 1.5 and 3 times higher than the reference carbon black supported catalysts. It was found that the silica particles as a catalyst support have a significant effect on reduction of methanol crossover and control of fuel feeding. Such a high performance in the operation with high concentrations was confirmed in the long-term durability test.     

Synthesis and characterization of carbon nanotubes supported platinum nanocatalyst for proton exchange membrane fuel cells

Multi-walled carbon nanotubes (MWCNTs) were used as catalyst support for depositing platinum nanoparticles by a wet chemistry route. MWCNTs were initially surface modified by citric acid to introduce functional groups which act as anchors for metallic clusters. A two-phase (water-toluene) method was used to transfer PtCl₆²⁻ from aqueous to organic phase and the subsequent sodium formate solution reduction step yielded Pt nanoparticles on MWCNTs. High-resolution TEM images showed that the platinum particles in the size range of 1-3 nm are homogeneously distributed on the surface of MWCNTs. The Pt/MWCNTs nanocatalyst was evaluated in the proton exchange membrane (PEM) single cell using H₂/O₂ at 80 °C with Nafion-212 electrolyte. The single PEM fuel cell exhibited a peak power density of about 1100 mW cm⁻² with a total catalyst loading of 0.6 mg Pt cm⁻² (anode: 0.2 mg Pt cm⁻² and cathode: 0.4 mg Pt cm⁻²). The durability of Pt/MWCNTs nanocatalyst was evaluated for 100 h at 80 °C at ambient pressure and the performance (current density at 0.4 V) remained stable throughout. The electrochemically active surface area (64 m² g⁻¹) as estimated by cyclic voltammetry (CV) was also similar before and after the durability test.     

Electroactivity of high performance unsupported Pt–Ru nanoparticles in the presence of hydrogen and carbon monoxide

The electrochemical activity of high performance unsupported (1:1) Pt–Ru electrocatalyst in the presence of hydrogen and carbon monoxide has been studied using the thin-film rotating disk electrode (RDE) technique. The kinetic parameters of these reactions were determined in H₂- and CO-saturated 0.5 M H₂SO₄ solutions by means of cyclic voltammetry, including CO stripping, and RDE voltammetry. Pt–Ru/Nafion inks were prepared in one step with different Nafion mass fractions, allowing determining the ionomer influence in electrocatalytic response and obtaining the kinetic current density in absence of mass-transfer effects, being 41 and 12 mA cm² (geometrical area), for H₂ and CO oxidation, respectively. These values correspond to mass activities of 1.37 and 0.40 A mg_Pt¹ and to specific activities of 1.52 and 0.44 mA cm_Pt². The Tafel analysis confirmed that hydrogen oxidation was a two-electron reversible reaction, while CO oxidation exhibited an irreversible behavior with a charge-transfer coefficient of 0.42. The kinetic results for CO oxidation are in agreement with the bifunctional theory, in which the reaction between Pt–CO and Ru–OH is the rate-determining step. The exchange current density for hydrogen reaction was 0.28 mA cm² (active surface area), thus showing similar kinetics to those found for carbon-supported Pt and Pt–Ru electrocatalyst nanoparticles.     

Highly fluorinated comb-shaped copolymer as proton exchange membranes (PEMs): Fuel cell performance

The fuel cell performance (DMFC and H₂/air) of highly fluorinated comb-shaped copolymer is reported. The initial performance of membrane electrode assemblies (MEAs) fabricated from comb-shaped copolymer containing a side-chain weight fraction of 22% are compared with those derived from Nafion and sulfonated polysulfone (BPSH-35) under DMFC conditions. The low water uptake of comb copolymer enabled an increase in proton exchange site concentrations in the hydrated polymer, which is a desirable membrane property for DMFC application. The comb-shaped copolymer architecture induces phase separated morphology between the hydrophobic fluoroaromatic backbone and the polysulfonic acid side chains. The initial performance of the MEAs using BPSH-35 and Comb 22 copolymer were comparable and higher than that of the Nafion MEA at all methanol concentrations. For example, the power density of the MEA using Comb 22 copolymer at 350 mA cm⁻² and 0.5 M methanol was 145 mW cm⁻², whereas the power densities of MEAs using BPSH-35 were 136 mW cm⁻². The power density of the MEA using Comb 22 copolymer at 350 mA cm⁻² and 2.0 M methanol was 144.5 mW cm⁻², whereas the power densities of MEAs using BPSH-35 were 143 mW cm⁻².     

Direct borohydride fuel cell using Ni-based composite anodes

In this study, nickel-based composite anode catalysts consisting of Ni with either Pd on carbon or Pt on carbon (the ratio of Ni:Pd or Ni:Pt being 25:1) were prepared for use in direct borohydride fuel cells (DBFCs). Cathode catalysts used were 1 mg cm⁻² Pt/C or Pd electrodeposited on activated carbon cloth. The oxidants were oxygen, oxygen in air, or acidified hydrogen peroxide. Alkaline solution of sodium borohydride was used as fuel in the cell. High power performance has been achieved by DBFC using non-precious metal, Ni-based composite anodes with relatively low anodic loading (e.g., 270 mW cm⁻² for NaBH₄/O₂ fuel cell at 60 °C, 665 mW cm⁻² for NaBH₄/H₂O₂ fuel cell at 60 °C). Effects of temperature, oxidant, and anode catalyst loading on the DBFC performance were investigated. The cell was operated for about 100 h and its performance stability was recorded.     

Inkjet printing of carbon supported platinum 3-D catalyst layers for use in fuel cells

We present a method of using inkjet printing (IJP) to deposit catalyst materials onto gas diffusion layers (GDLs) that are made into membrane electrode assemblies (MEAs) for polymer electrolyte fuel cell (PEMFC). Existing ink deposition methods such as spray painting or screen printing are not well suited for ultra low (<0.5 mg Pt cm⁻²) loadings. The IJP method can be used to deposit smaller volumes of water based catalyst ink solutions with picoliter precision provided the solution properties are compatible with the cartridge design. By optimizing the dispersion of the ink solution we have shown that this technique can be successfully used with catalysts supported on different carbon black (i.e. XC-72R, Monarch 700, Black Pearls 2000, etc.). Our ink jet printed MEAs with catalyst loadings of 0.020 mg Pt cm⁻² have shown Pt utilizations in excess of 16,000 mW mg⁻¹ Pt which is higher than our traditional screen printed MEAs (800 mW mg⁻¹ Pt). As a further demonstration of IJP versatility, we present results of a graded distribution of Pt/C catalyst structure using standard Johnson Matthey (JM) catalyst. Compared to a continuous catalyst layer of JM Pt/C (20% Pt), the graded catalyst structure showed enhanced performance.     

LaNi0.8Co0.2O3 as a cathode catalyst for a direct borohydride fuel cell

A perovskite-type oxide LaNi_0.8Co_0.2O₃ is prepared as a direct borohydride fuel cell (DBFC) cathode catalyst. Its electrochemical properties are studied by cyclic voltammetry. The results demonstrate that LaNi_0.8Co_0.2O₃ exhibits excellent electrochemical activity with respect to the oxygen reduction reaction (ORR) and good tolerance of BH₄⁻ ions. Maximum power densities of 114.5 mW cm⁻² at 30 °C and 151.3 mW cm⁻² at 62 °C are obtained, and good stability (300-h stable performance at 20 mA cm⁻²) is also exhibited, which shows that such perovskite-type oxides as LaNi_0.8Co_0.2O₃ can be excellent catalysts for DBFCs.     

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.     

Development of high performance carbon composite catalyst for oxygen reduction reaction in PEM Proton Exchange Membrane fuel cells

Highly active and stable carbon composite catalysts for oxygen reduction in PEM fuel cells were developed through the high-temperature pyrolysis of Co–Fe–N chelate complex, followed by the chemical post-treatment. A metal-free carbon catalyst was used as the support. The carbon composite catalyst showed an onset potential for oxygen reduction as high as 0.87 V (NHE) in H₂SO₄ solution, and generated less than 1% H₂O₂. The PEM fuel cell exhibited a current density as high as 0.27 A cm⁻² at 0.6 V and 2.3 A cm⁻² at 0.2 V for a catalyst loading of 6.0 mg cm⁻². No significant performance degradation was observed over 480 h of continuous fuel cell operation with 2 mg cm⁻² catalyst under a load of 200 mA cm⁻² as evidenced by a resulting cell voltage of 0.32 V with a voltage decay rate of 80 μV h⁻¹. Materials characterization studies indicated that the metal–nitrogen chelate complexes decompose at high pyrolysis temperatures above 800 °C, resulting in the formation of the metallic species. During the pyrolysis, the transition metals facilitate the incorporation of pyridinic and graphitic nitrogen groups into the carbon matrix, and the carbon surface doped with nitrogen groups is catalytically active for oxygen reduction.     

Recovery of borohydride from metaborate solution using a silver catalyst for application of direct rechargable borohydride/peroxide fuel cells

This study aims at the investigation of a suitable catalyst for the electrochemical reduction mechanism of metaborate into borohydride with the hope of the construction of rechargeable direct borohydride/peroxide fuel cell. A passive direct borohydride/peroxide fuel cell with Ag anode and Pt/C cathode was constructed. Its maximum power density was calculated as 7 mW cm⁻² at a cell voltage of 0.5 and a current density of 11 mA cm⁻². Recycling of the metaborate, the co-product of the borohydride oxidation, to the borohydride is the major issue in order to achieve the rechargeable borohydride fuel cells. Accordingly, the NaBO₂ solution was electrolyzed with the use of Ag electrodes for this purpose. The converted borohydride were determined by the cyclic voltammetry using Au and Ag electrodes which are highly selective for this purpose. The cyclic voltammetric curves revealed the peaks which indicated the conversion of NaBO₂ into NaBH₄. The presence of NaBH₄ was also verified iodometrically after the electrolysis. It was observed that there was 10% conversion after 24 h of electrolysis which reached up to 17% after 48 h. These data are very promising in the quest of the construction of a rechargeable direct borohydride fuel cell.     

Cathode development for alkaline fuel cells based on a porous silver membrane

Porous silver membranes were investigated as potential substrates for alkaline fuel cell cathodes by the means of polarization curves and electrochemical impedance spectroscopy measurements. The silver membranes provide electrocatalytic function, mechanical support and a means of current collection. Improved performance, compared to a previous design, was obtained by increasing gas accessibility (using Teflon AF instead of PTFE suspension) and by adding a catalyst (MnO₂ or Pt) in the membrane structure to increase the cathode activity. This new cathode design performed significantly better (∼55 mA cm⁻² at 0.8 V, ∼295 mA cm⁻² at 0.6 V and ∼630 mA cm⁻² at 0.4 V versus RHE) than the previous design (∼30 mA cm⁻² at 0.8 V, ∼250 mA cm⁻² at 0.6 V and ∼500 mA cm⁻² at 0.4 V) in the presence of 6.9 M KOH and oxygen (1 atm(abs)) at room temperature. The hydrophobisation technique of the porous structure and the addition of an extra catalyst appeared to be critical and necessary to obtain high performance. A passive air-breathing hydrogen-air fuel cell constructed from the membranes achieves a peak power density of 65 mW cm⁻² at 0.40 V cell potential when operating at 25 °C showing a 15 mW cm⁻² improvement compared to the previous design.     

Performance of a miniaturized silicon reformer-PrOx-fuel cell system

A fuel cell made with silicon is operated with hydrogen supplied by a reformer and a preferential oxidation (PrOx) reactor those are also made with silicon. The performance and durability of the fuel cell is analyzed and tested, then compared with the results obtained with pure hydrogen. Three components of the system are made using silicon technologies and micro electro-mechanical system (MEMS) technology. The commercial Cu-ZnO-Al₂O₃ catalyst for the reformer and the Pt-Al₂O₃ catalyst for the PrOx reactor are coated by means of a fill-and-dry method. A conventional membrane electrode assembly composed of a 0.375 mg cm⁻² PtRu/C catalyst for the anode, a 0.4 mg cm⁻² Pt/C catalyst for the cathode, and a Nafion™ 112 membrane is introduced to the fuel cell. The reformer gives a 27 cm³ min⁻¹ gas production rate with 3177 ppm CO concentration at a 1 cm³ h⁻¹ methanol feed rate and the PrOx reactor shows almost 100% CO conversion under the experimental conditions. Fuel cells operated with this fuel-processing system produce 230 mW cm⁻² at 0.6 V, which is similar to that obtained with pure hydrogen.     

Carbon-supported Ir–V nanoparticle as novel platinum-free anodic catalysts in proton exchange membrane fuel cell

The active, carbon-supported Ir–V nanoparticle catalysts were successfully synthesized using IrCl₃ and NH₄VO₃ as the Ir and V precursors in ethylene glycol refluxing at 120 °C with varying pH values, then further reduction under hydrogen atmosphere at 200 °C. The nanostructured catalysts were characterized by X-ray diffraction (XRD) and high resolution transmission electron microscopy (TEM). These carbon-supported catalysts give a good dispersion of Ir–V/C electrocatalysts with mean particle size of 2–3 nm, thus leading to a marked promotion of hydrogen oxidation reaction. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry techniques (CV) were used to characterize on-line the performance of the proton exchange membrane fuel cell (PEMFC) using several anode catalysts at different pH values. It was found that the pH value for the synthesis of catalysts affects the performance of electrocatalysts significantly, based on the discharge characteristics of the fuel cell. High cell performance on the anode was achieved with a loading of 0.4 mg cm⁻² 40%Ir–10%V/C catalyst synthesized at pH 12, which results in a maximum a power density of 1008 mW cm⁻² at 0.6 V and 70 °C. This is 50% higher performance than that for commercial available Pt/C catalyst. Fuel cell life test at a constant current density of 1000 mA cm⁻² demonstrated an initial stability up to 100 h generating a cell voltage of 0.6 V, which strongly suggests that the novel Ir–V/C nanoparticle catalysts proposed in this work could be promising for PEMFC.     

Investigations on high performance proton exchange membrane water electrolyzer

In order to improve proton exchange membrane water electrolyzer (PEMWE) performance, some factors related to the processes of preparing the Membrane Electrode Assemblies (MEAs), such as iridium (Ir) electrocatalyst loading and Nafion^® content at the anode, thicknesses of proton exchange membrane and gas diffusion layers (GDLs), were examined. In addition, a home-made supported Ir/titanium carbide (Ir/TiC, 20% Ir by weight) was developed for the anode. With best commercial Ir catalyst loading of 1.5 mg cm⁻² Ir at the anode, the cell's current densities of 1346 mA cm⁻², 1820 mA cm⁻² and 2250 mA cm⁻² were achieved at the cell potentials of 1.80 V, 1.90 V and 2.00 V, respectively. A PEMWE with 0.3 mg cm⁻² Ir loading of Ir/TiC anode catalyst was comparatively stable and gave current densities of 840 mA cm⁻², 1130 mA cm⁻² and 1463 mA cm⁻² at the cell potentials of 1.80 V, 1.90 V and 2.00 V, respectively. Based on catalysis efficiency of Amperes per milligram of Ir, the Ir/TiC catalyst is found to be more active than unsupported Ir catalyst.     

Effects of operation conditions on direct borohydride fuel cell performance

In this study, the influences of different operational conditions such as cell temperature, sodium hydroxide concentration, oxidant conditions and catalyst loading on the performance of direct borohydride fuel cell which consisted of Pd/C anode, Pt/C cathode and Na⁺ form Nafion membrane as the electrolyte were investigated. The experimental results showed that the power density increased by increasing the temperature and increasing the flow rate of oxidant. Furthermore, it was found that 20 wt.% of NaOH concentration was optimum for DBFC operation. When oxygen was used as oxidant instead of air, better performance was observed. Experiments also showed that electrochemical performance was not considerably affected by humidification levels. An enhanced power density was found by increasing the loading of anodic catalyst. In the present study, a maximum power density of 27.6 mW cm⁻² at a cell voltage of 0.85 V was achieved at 55 mA cm⁻² at 60 °C when humidified air was used.     

A comparative study of electrochemical methods on Pt–Ru DMFC anode catalysts: The effect of Ru addition

In the present study comparative electrochemical study of methanol electro-oxidation reaction, the effect of ruthenium addition and experimental parameters on methanol electro-oxidation reaction at high performance carbon supported Pt and Pt–Ru catalysts have been studied by cyclic voltammetry (CV), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS) in H₂SO₄ (0.05–2.00 M) + CH₃OH (0.01–4.00 M) at 20–70 °C. Tafel plots for the methanol oxidation reaction on Pt and Pt–Ru catalysts show reasonably well-defined linear region with the slopes of 128–174 mV dec⁻¹(α = 0.34–0.46). The activation energies from Arrhenius plots have been found as 39.06–50.65 kJ mol⁻¹. As a result, methanol oxidation is enhanced by the addition of ruthenium. Furthermore, Pt–Ru (25:1) catalyst shows best electro–catalytic activity, higher resistance to CO, and better long term stability compared to Pt–Ru (3:1), Pt–Ru (1:1), and Pt. Finally, the EIS measurements on Pt–Ru (25:1) catalyst reveals that methanol electro-oxidation reaction consists of two process: methanol dehydrogenation step at low potentials (<700 mV) and the oxidation removal of CO_ads by OH_ads at higher potentials (>700 mV).