Carbon supported Ag nanoparticles with different particle size as cathode catalysts for anion exchange membrane direct glycerol fuel cells

The effect of Ag particle size on oxygen reduction reaction (ORR) at the cathode was investigated in anion exchange membrane direct glycerol fuel cells (AEM-DGFC) with oxygen as an oxidant. At the anode, high purity glycerol (99.8 wt%) or crude glycerol (88 wt%, from soybean biodiesel) was used as fuel, and commercial Pt/C served as the anode catalyst. A solution phase-based nanocapsule synthesis method was successfully developed to prepare the non-precious Ag/C cathode catalyst, with LiBEt₃H as a reducing agent. XRD and TEM characterizations show that as-synthesized Ag nanoparticles (NP) with a size of 2–9 nm are well dispersed on the Vulcan XC-72 carbon black support. Commercial Ag nanoparticles with a size of 20–40 nm were also supported on carbon black as a control sample. The results show that higher peak power density was obtained in AEM-DGFC employing an Ag-NP catalyst with smaller particle size: nanocapsule made Ag-NP > commercial Ag-NP (Alfa Aesar, 99.9%). With the nanocapsule Ag-NP cathode catalyst, the peak power density and open circuit voltage (OCV) of AEM-DGFC with high-purity glycerol at 80 °C are 86 mW cm⁻² and 0.73 V, respectively. These are much higher than 45 mW cm⁻² and 0.68 V for the AEM-DGFC with the commercial Ag/C cathode catalyst, which can be attributed to the enhanced kinetics and reduced internal resistance. Directly fed with crude glycerol, the AEM-DGFC with the nanocapsule Ag-NP cathode catalyst shows an encouraging peak power density of 66 mW cm⁻², which shows great potential of direct use of biodiesel waste fuel for electricity generation.     

Borohydride electrochemical oxidation on carbon-supported Pt-modified Au nanoparticles

The carbon-supported Pt-modified Au nanoparticles were prepared by two different chemical reduction processes, the simultaneous chemical reduction of Pt and Au on carbon process (A-AuPt/C) and the successive reduction of Au then Pt (B-AuPt/C) on carbon process. These two catalysts were investigated as the anode catalysts for a direct borohydride fuel cell (DBFC) and Au nanoparticles on carbon (Au/C) were also prepared for comparison. The DBFC with B-AuPt/C as the anode catalyst shows the best anode and fuel cell performance. The maximum power density with the B-AuPt/C catalyst is 112 mW cm⁻² at 40 °C, compared to 97 mW cm⁻² for A-AuPt/C and 65 mW cm⁻² for Au/C. In addition, the DBFC with the B-AuPt/C catalyst shows the best fuel utilization with a maximum apparent number of electrons (N_app) equal to 6.4 in 1 M NaBH₄ and 7.2 in 0.5 M NaBH₄ as compared to the value of N_app of 8 for complete utilization of borohydride.     

Synthesis and characterization of Pt-Au/C catalyst for glucose electro-oxidation for the application in direct glucose fuel cell

To minimize the poisoning of Pt-catalyst in glucose electro-oxidation for direct glucose fuel cell, carbon supported low metal loaded platinum-gold (Pt-Au/C) catalyst (1:1) was synthesized by immobilizing metal sols on carbon. The physical characterization of Pt-Au/C, Pt/C and Au/C was carried out using transmission electron microscope (TEM), scanning electron microscope (SEM), energy dispersive X-ray (EDX), X-ray diffraction (XRD) and thermo gravimetric analysis (TGA). SEM indicates the uniformity in loading of metals on Vulcan XC-72 carbon support, whereas TEM picture and XRD pattern confirm the formation of Pt-Au nanoparticles of less than 10 nm size. TGA shows the metal present in Pt-Au/C catalyst is 14.5% by wt. Electrochemical analysis such as cyclic voltammetry (CV) and chronoamperometry (CA) on Pt-Au/C and commercial Pt/C and Au/C (40 wt. % of metal) for glucose electro-oxidation in alkaline media shows that Pt-Au/C is capable of electro-oxidation of glucose at low potential as that of Pt/C catalyst and more active than Au/C catalyst. The poisoning rate of prepared Pt-Au/C (0.0046% s⁻¹) is lower than that of Pt-Ru/C (0.0085% s⁻¹) and Pt/C (0.011% s⁻¹) catalysts. A batch cell operated using Pt-Au/C as anode and activated charcoal as cathode delivered 0.9 V OCV and 0.72 mW cm⁻² peak power density at 0.2 M glucose in 1 M KOH solution.     

Preparation and characterization of nanoporous carbon-supported platinum as anode electrocatalyst for direct borohydride fuel cell

The nanoporous carbon (NPC) is synthesized by carbonization of metal–organic framework-5 (MOF-5, [Zn₄O(bdc)₃], bdc = 1,4-benzenedicarboxylate) with furfuryl alcohol (FA) as carbon source and used as the carrier of the anode catalyst for the direct borohydride–hydrogen peroxide fuel cell (DBHFC). Then the NPC-supported Pt anode catalyst (Pt/NPC) is firstly prepared by a modified NaBH₄ reduction method. The obtained Pt/NPC catalyst is characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), energy dispersive spectrometry (EDS), cyclic voltammetry, chronopotentiometry, chronoamperometry and fuel cell test. The results show that the Pt/NPC is made up of the spherical Pt nanoparticles which disperse uniformly on the surface of the NPC with average size 2.38 nm, and exhibits 36.38% higher current density for directly borohydride oxidation than the Vulcan XC-72 carbon supported Pt (Pt/XC-72). Besides, the DBHFC using the Pt/NPC as anode electrocatalyst shows the maximum power density as high as 54.34 mW cm⁻² at 25 °C.     

The effect of electrode parameters on the performance of anion exchange polymer membrane fuel cells

An investigation of several electrode parameters on performance of an alkaline membrane fuel cell is described. The studied parameters were: ionomer content, anode and cathode catalyst layer thickness, electrode aminating agent and membrane thickness.It was found that an optimum ionomer content depended on a balance between the OH⁻ ion/water mobility and the oxygen solubility/diffusivity through it and which varied with temperature. Thick catalyst layers were necessary for the anode as thin anode catalyst layers suffered from flooding. 40%Pt/C provided the best thickness (with loading of 0.4 mg_Pt cm⁻²) for cathodes operating with air.An aminated low density poly(ethylene-co-vinyl benzyl chloride) (LDPE-VBC) membrane was shown to be a good membrane for an alkaline membrane fuel cell, giving conductivities up to 0.13 S cm⁻¹ at 80 °C. A Membrane Electrode Assembly (MEA) utilizing this membrane with fully hydrated thickness of 57 μm produced good peak power density, at a high potential of 500 mV, of 337 mW cm⁻² with air (1 bar gauge) at 60 °C.     

High activity of Au-Cu/C electrocatalyst as anodic catalyst for direct borohydride-hydrogen peroxide fuel cell

Carbon supported Au-Cu bimetallic nanoparticles are prepared by a modified NaBH₄ reduction method in aqueous solution at room temperature. The electrocatalytic activities of the Au-Cu/C catalysts are investigated by cyclic voltammetry, chronoamperometry, chronopotentiometry and fuel cell experiments. It has been found that the Au-Cu/C catalysts have much higher catalytic activity for the direct oxidation of BH₄⁻ than Au/C catalyst. Especially, the Au₆₇Cu₃₃/C catalyst presents the highest catalytic activity for BH₄⁻ electrooxidation among all as-prepared catalysts, and the DBHFC using Au₆₇Cu₃₃/C anode catalyst and Au/C cathode catalyst shows the maximum power density of 51.8 mW cm⁻² at 69.5 mA cm⁻² and 20 °C.     

Highly active 40 wt.% PtRu/C anode electrocatalysts for PEMFCs prepared by an improved impregnation method

Highly active 40 wt.% PtRu/C electrocatalysts that can be used as anode in polymer electrolyte membrane fuel cells (PEMFCs) were fabricated by improved impregnation method that introduced formaldehyde as a reducing agent and HCl as a segmentation agent with heat treatments at various temperatures. The morphology of the prepared catalysts was characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD), which revealed that the PtRu particles on carbon after heat treatment at 300 °C had a very narrow size distribution in the range of 1.5-3.4 nm, and that the average size varied between 2.3 and 2.4 nm. The electrochemical active surface area of the prepared PtRu/C catalysts was determined by CO-stripping voltammetry. In particular, the PtRu nanostructure electrodes heat treated at 300 °C showed an excellent catalytic activity because of the metals’ large surface area as well as a sufficient degree of alloy formation for CO tolerance. The unit cell performance of the PtRu/C catalyst with heat treatment at 300 °C exhibited a power density of 0.67 W cm⁻² which was higher than that of a unit cell with a commercial PtRu/C catalyst (E-TEK) with the same metal loadings.     

Numerical analysis of anion-exchange membrane direct glycerol fuel cells under steady state and dynamic operations

This work develops a one-dimensional model of an alkaline anion-exchange membrane direct glycerol fuel cell (AEM-DGFC) for cogeneration of tartronate and electricity. The model is validated against steady state and dynamic experiments, and shows good agreement. Steady state modeling includes anode and cathode losses and predicts the single cell polarization and power density curves. Coupled mass transport, charge transport, and electrochemical kinetics predict the effects of varying reactant concentration and diffusion layer porosity on single cell performance. The results show that anode overpotential is the major source of loss at middle to high current density regions, due to limited glycerol diffusion at the catalyst layer. Furthermore, the dynamic response of AEM-DGFC to step changes in current density is simulated by considering time-dependent species transport and double-layer capacitance charging. Analysis of dynamic simulation reveals that the liquid-phase reactant diffusion is a key factor influencing the transient AEM-DGFC behavior and is very sensitive to diffusion layer design. This new numerical analysis of a glycerol-fed fuel cell demonstrates that a simple, single oxidation product model can successfully predict the steady state and dynamic losses.     

Preparation of Pt nanoparticles on carbon support using modified polyol reduction for low-temperature fuel cells

Highly dispersed Pt nanoparticles supported on Vulcan XC-72R were prepared by a modified polyol reduction for low-temperature fuel cells. The modified polyol reduction was controlled with various concentrations of reducing agent and reduction times at 90 °C. The 20 wt% Pt/C catalyst prepared under an optimum reduction condition (reduction temperature = 90 °C, ethylene glycol/H₂O volume ratio = 1, and reduction time = 10 h) exhibited the highest electrochemical active surface area (EAS) and methanol oxidation activity due to the small Pt nanoparticles (1.2 nm) with quite a narrow size distribution between 0.5 and 2 nm. The 40 wt% Pt/C catalyst was prepared using the optimum condition to confirm the applicability of the preparation method. The synthesized 40 wt% Pt/C catalyst had smaller-sized Pt nanoparticles (1.3 nm) and a higher EAS than that of a commercial 40 wt% Pt/C catalyst. With pure H₂ (anode) and air (cathode), a PEMFC using the synthesized 40 wt% Pt/C catalyst as a cathode had higher single-cell performance than that of the commercial catalyst.     

The study of Au/MoS2 anode catalyst for solid oxide fuel cell (SOFC) using H2S-containing syngas fuel

Au/MoS₂ is a promising anode catalyst for conversion of all components of H₂S-containing syngas in solid oxide fuel cell (SOFC). MoS₂-supported nano-Au particles have catalytic activity for conversion of CO when syngas is used as fuel in SOFC systems, thus preventing poisoning of MoS₂ active sites by CO. In contrast to use of MoS₂ as anode catalyst, performance of Au/MoS₂ anode catalyst improves when CO is present in the feed. Current density over 600 mA cm⁻² and maximum power density over 70 mW cm⁻² were obtained at 900 °C, showing that Au/MoS₂ could be potentially used as sulfur-tolerant catalyst in fuel cell applications.     

Ir-Pt/C composite with high metal loading as a high-performance anti-reversal anode catalyst for proton exchange membrane fuel cells

Voltage reversal induced by hydrogen starvation can severely corrode the anode catalyst support and deteriorate the performance of proton exchange membrane fuel cells. A material-based strategy is the inclusion of an oxygen evolution reaction catalyst (e.g., IrO₂) in the anode to promote water electrolysis over harmful carbon corrosion. In this work, an Ir-Pt/C composite catalyst with high metal loading is prepared. The membrane-electrode-assembly (MEA) with 80 wt% Ir-Pt(1:2)/C shows a first reversal time (FRT) of up to 20 hours, which is about ten times that of MEA with 50 wt% Ir-Pt(1:2)/C does. Furthermore, the MEA with 80 wt% Ir-Pt(1:2)/C exhibits a minimum cell voltage loss of 6 mV@1 A/cm² when the FRT is terminated in 2 hours, in which the MEA with 50 wt% Ir-Pt(1:2)/C exhibits a voltage loss of 105 mV@1 A/cm². Further physicochemical and electrochemical characterizations demonstrate that the destruction of anode catalyst layer caused by the voltage reversal process is alleviated by the use of the composite catalyst with high metal loading. Hence, our results reveal that the combination of OER catalyst on the Pt/C with high metal loading is a promising approach to alleviate the degradation of anode catalyst layer during the voltage reversal process for PEMFCs.     

Electrocatalysts supported on multiwalled carbon nanotubes for direct borohydride–hydrogen peroxide fuel cell

Electrocatalysts of Rh, Ru, Pt, Au, Ag, Pd, Ni, and Cu supported on multiwalled carbon nanotubes for direct borohydride–hydrogen peroxide fuel cells are investigated. Metal/γ-Al₂O₃ catalysts for NaBH₄ and H₂O₂ decomposition tests are manufactured and their catalytic activities upon decomposition are compared. Also, the effects of XC-72 and multiwalled carbon nanotube (MWCNT) carbon supports on fuel cell performance are determined. The performance of the catalyst with MWCNTs is better than that of the catalyst with XC-72 owing to a large amount of reduced Pd and the good electrical conductivity of MWCNTs. Finally, the effect of electrodes with various catalysts on fuel cell performance is investigated. Based on test results, Pd (anode) and Au (cathode) are selected as catalysts for the electrodes. When Pd and Au are used together for electrodes, the maximum power density obtained is 170.9 mW/cm² (25 °C).     

Glycerol oxidation in solid oxide fuel cells based on a Ni-perovskite electrocatalyst

An investigation of the electrochemical oxidation of glycerol as alternative to hydrogen and methane in solid oxide fuel cells (SOFCs) based on a noble metal-free anode catalyst was carried out. The anode electrocatalyst consisted of a Ni-modified La_0.6Sr_0.4Fe_0.8Co_0.2O₃ (LSFCO) perovskite. After thermal activation, air treatment at 1100 °C followed by reduction at 800 °C in H₂, Ni was mainly present as ultrafine La₂NiO₄ particles homogeneously dispersed on the perovskite surface. The thermal activation also caused a modification of perovskite into a lanthanum depleted structure. The thermal reduction at 800 °C determined the occurrence of metallic Ni on the surface. These results were corroborated by X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and X-ray diffraction (XRD). A suitable power density (327 mW cm⁻²) was achieved for the electrolyte supported SOFC fed with chemical-grade glycerol in almost dry condition, i.e. steam to carbon ratio (S/C) of 0.2. The highest electrical efficiency (voltage efficiency) approached 50% at the peak power under mild humidification (S/C = 0.2). Whereas an increase of water to glycerol ratio, caused a progressive decrease of voltage efficiency at the peak power down to 44% for S/C = 2.     

Synthesis and evaluation of Pt/rGO as the anode electrode in abiotic glucose fuel cell: Near to the human body physiological condition

In this research, abiotic catalyst 40 wt% Pt/rGO is successfully synthesized via chemical reduction method with an average particle size of 3 nm (characterized by TEM and XRD), and activity of it as anode catalyst for glucose oxidation is evaluated in phosphate-buffered saline (PBS, pH = 7.4) in the presence of 5 mM glucose (near-human body physiological concentrations).The fuel cell testing is carried out in a two-chamber abiotic glucose fuel cell (AGFC) utilizing Pt/rGO as the anode catalyst and PBS/glucose as the feed. Furthermore, effect of circulated fuel (based on human arm's vein blood flow rate, 0.33 mLs⁻¹) is also investigated for implantable purposes and is compared to stationary fuel; 10% increase in the AGFC voltage in contrast to 23% cell voltage drop respectively under 0.01 mAcm⁻² current density over 15 h. Results indicate that Pt/rGO is a promising catalyst for AGFCs to power implantable devices.     

High Performance plasma sputtered PdPt fuel cell electrodes with ultra low loading

A PdPt (10 wt% Pt) catalyst is used to replace platinum at the cathode of a proton exchange membrane fuel cell membrane electrode assembly (PEMFC MEA) whereas pure palladium is used as the anode catalyst. The catalysts are deposited on commercial carbon woven web and carbon paper GDLs by plasma sputtering. The relations between the depth density profiles, the electrode support and the fuel cell performances are discussed. It is shown that the catalyst gradient is an important parameter which can be controlled by the catalyst depth density profile and/or the choice of electrode support. An optimised electrode structure has been obtained, which allows limiting the platinum requirement. Under suitable conditions of a working PEMFC (80 °C and 3 bar absolute pressure), very high catalysts utilization is obtained at both electrodes, leading to 250 kW g_Pt⁻¹ and 12.5 kW g_Pd⁻¹ with a monocell fitted with a PdPt (10:1 weight ratio) cathode and a pure Pd anode.     

Effect of Nafion aggregation in the anode catalytic layer on the performance of a direct formic acid fuel cell

The effect of Nafion ionomer aggregation within the anode catalytic layer for a direct formic acid fuel cell (DFAFC) has been investigated. By simple heat treatment, the aggregation states of Nafion ionomers in aqueous solution can be tuned. Nafion agglomerate sizes in the solution decrease and aggregate size distribution becomes narrow with the increase in heat-treatment temperature. At a heat-treatment temperature of ca. 80 °C, nearly monodispersed Nafion ionomers corresponding to an aggregate size of ca. 25 nm in the solution are observed. The use of small Nafion ionomer agglomerates in the Nafion solution for anode catalytic layer significantly improves the performance of the passive DFAFCs. Impedance analysis indicates that the increased performance of the passive DFAFC with the anode using Nafion solution pretreated at elevated temperatures could be attributed to the decrease in charge-transfer resistance of the anode reaction. The decrease in Nafion aggregation within the catalyst ink leads to an increase in Nafion ionomer utilization within the catalyst layer and an improvement in catalyst utilization; thus enabling us to decrease Nafion loading within the anode catalytic layer but with slight improvement in DFAFC's performance.     

A single-component fuel cell reactor

We report here a single-component reactor consisting of a mixed ionic and semi-conducting material exhibiting hydrogen-air (oxygen) fuel cell reactions. The new single-component device was compared to a conventional three-component (anode/electrolyte/cathode) fuel cell showing at least as good performance. A maximum power density of 300-600 mW cm⁻² was obtained with a LiNiZn-oxide and ceria-carbonate nanocomposite material mixture at 450-550 °C. Adding a redox catalyst element (Fe) resulted in an improvement reaching 700 mW cm⁻² at 550 °C.     

Performance and degradation of high temperature polymer electrolyte fuel cell catalysts

An investigation of carbon-supported Pt/C and PtCo/C catalysts was carried out with the aim to evaluate their stability under high temperature polymer electrolyte membrane fuel cell (PEMFC) operation. Carbon-supported nanosized Pt and PtCo particles with a mean particle size between 1.5 nm and 3 nm were prepared by using a colloidal route. A suitable degree of alloying was obtained for the PtCo catalyst by using a carbothermal reduction. The catalyst stability was investigated to understand the influence of carbon black corrosion, platinum dissolution and sintering in gas-fed sulphuric acid electrolyte half-cell at 75 °C and in PEMFC at 130 °C. Electrochemical active surface area and catalyst performance were determined in PEMFC at 80 °C and 130 °C. A maximum power density of about 700 mW cm⁻² at 130 °C and 3 bar abs. O₂ pressure with 0.3 mg Pt cm⁻² loading was achieved. The PtCo alloy showed a better stability than Pt in sulphuric acid after cycling; yet, the PtCo/C catalyst showed a degradation after the carbon corrosion test. The PtCo/C catalyst showed smaller sintering effects than Pt/C after accelerated degradation tests in PEMFC at 130 °C.     

Promoting formic acid and ethylene glycol electrooxidation activity on Ga modified Pd based catalysts

Herein, carbon nanotube (CNT)-supported Ga@PdAgCo catalysts were synthesized by sodium borohydride (SBH) sequential reduction method. These catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma-mass spectrometry (ICP-MS). Characterization results revealed that these catalysts were succesfully preared at desired loading and atomic ratios. From the XRD pattern, the crystallite size of 0.5% Ga@PdAgCo(80:10:10)/CNT catalysts was found as 6.95 nm by utilizing the Scherrer equation. From TEM measurements, the average particle sizes of Pd/CNT, PdAgCo(80:10:10)/CNT, and 0.5% Ga@PdAgCo(80:10:10)/CNT catalysts were found to be 54 nm, 25 nm, and 7 nm, respectively. It is clear that particle sizes obtained from TEM and XRD were close to eachother. Electrochemical impedance spectroscopy (EIS), chronoamperometry (CA), and cyclic voltammetry (CV) measurements were realized to examine the formic acid and ethylene glycol electrooxidation performances of catalysts. 0.5% Ga@PdAgCo(80:10:10/CNT) and 7% Ga@PdAgCo(80:10:10/CNT) catalysts had the best specific activity and mass activity as 3.37 mA/cm² (297.61 mA/mg Pd) and 4.95 mA/cm² (462.59 mA/mg Pd) for ethylene glycol and formic acid electrooxidation, respectively. In addition, EIS results showed that Ga@PdAgCo(80:10:10/CNT) catalyst had a faster electron transfer rate via low charge transfer resistance. As a result, 0.5% Ga@PdAgCo(80:10:10/CNT) catalyst is a promising new anode catalyst for direct ethylene glycol fuel cells.     

Direct ammonia fuel cell performance using PtIr/C as anode electrocatalysts

Direct ammonia fuel cell (DAFC) performance was investigated using as anode PtIr/C electrocatalysts (Pt:Ir atomic ratios of 50:50, 70:30, 80:20 and 90:10) prepared by the borohydride reduction process and NH₄OH 1.0, 3.0 and 5.0 mol L⁻¹ in KOH 1.0 mol L⁻¹ as fuel. X-ray analyses of PtIr/C electrocatalysts suggested the formation of PtIr alloy and the transmission electron micrographs showed the average particle diameters between 4.5 and 6.0 nm. Using PtIr/C 50:50 electrocatalyst and NH₄OH 5.0 mol L⁻¹ in KOH 1.0 mol L⁻¹ at 40 °C a maximum power density was 48% and 70% higher than that obtained using Pt/C and Ir/C electrocatalysts, respectively. The increase of electroactivity using PtIr/C electrocatalysts might be related to a decrease of poisoning on catalyst surface by N_ads species and to an improved kinetic for ammonia oxidation reaction.