Characterization and single cell testing of Pt/C electrodes prepared by electrodeposition

Electrodes for proton exchange membrane fuel cells (PEMFC) have been prepared by the electrodeposition method. For this task, the electrodeposition of platinum is carried out on a carbon black substrate impregnated with an ionomer, proton conducting, medium. Before electrodeposition, the substrate is submitted to an activation process to increase the hydrophilic character of the surface to a few microns depth.Electrodeposition of platinum takes place inside the generated surface hydrophilic layer, resulting in a continuous phase covering totally or partially carbon substrate grains. Cross sectional images show a decay profile of platinum towards the interior of the substrate, reflecting a deposition process limited by diffusion of PtCl₆²⁻ through the porous substrate. Electrodes with different platinum loads have been prepared, and membrane electrode assemblies (MEA) have been mounted with the electrodeposited electrodes as cathode and other standard components (commercial anode and Nafion^R 117 membrane). The electrochemically active surface area determined from hydrogen underpotential deposition charge, is lower on the electrodeposited electrodes than on standard electrodes. However, single cell testing shows higher mass specific activity on electrodeposited cathodes with low and intermediate Pt load (below 0.05 mg Pt cm⁻²).     

Optimal topology and distribution of catalyst in PEMFC

The equations that govern the various transport phenomena occurring in a polymer electrolyte membrane fuel cell (PEMFC) were formulated and implemented in a commercial finite element software, in order to predict the fuel cell current density with respect to the operating conditions. The numerical model showed polarization curves in accordance with literature. The catalyst utilization was then improved by optimizing the platinum distribution (design variable) in the fuel cell, so as to maximize current density (objective function) for a fixed total amount of platinum (constraint). The first analysis showed that, for equal anode and cathode catalyst layer thicknesses, maximal current density was achieved by placing more catalyst in the cathode than in the anode. The second analysis showed that, for equal anode and cathode catalyst layer density, maximal current density was achieved by using a catalyst layer that is thicker on the cathode side than that on the anode side. Finally, a topological optimization of the platinum density within the cathode catalyst layer was performed with a gradient based algorithm, and the results showed that at a high stoichiometric ratio, the best design has most of its platinum placed where the reaction rate is the highest, i.e., close to the membrane layer.     

Activities of Pt/Sibunit-1562 catalysts in the ORR in PEMFC: Effect of Pt content and Pt load at cathode

In this paper, a systematic investigation was carried out of activities at 80 °C of Pt supported on Sibunit-1562 graphitized carbon in the electroreduction of oxygen in the polymer electrolyte fuel cell. Pt content in the Pt/Sibunit-1562 catalysts was 20, 40, and 60 wt.% and Pt load at the cathode was varied in the 200–6.25 μg_Pt cm⁻² interval. The results were compared with the activity of commercial 20 wt.% Pt/Vulcan XC-72 catalyst. To optimize the transport properties of the cathode layer and maintain its thickness upon using Pt/Sibunit −1562 catalysts with varied Pt content and Pt loads a definite amount of Vulcan-XC-72 carbon support was added to the cathode catalytic inks. Higher activity of Pt/Sibunit-1562 catalysts was found as compared to that of commercial 20 wt.% Pt/Vulcan XC-72 with similar particle size of the active component.     

Nanostructured platinum catalyst layer prepared by pulsed electrodeposition for use in PEM fuel cells

Nanostructured thin catalyst layer with uniform distribution of platinum particles on a GDL useful for PEM fuel cell was obtained by preferential pulsed electrodeposition (PED) from a dilute solution of chloroplatinic acid. A low platinum loading on the electrode was obtained by PED method, without any loss in fuel cell performance compared with electrodes prepared by conventional brush coating method. The electrodeposition was optimized by varying the duty cycle and current density. The fuel cell performance was found to be 350 mA/cm² at an operating voltage of 0.6 V at 60 °C with hydrogen and air as reactants at ambient pressure. The nanostructured thin catalyst layer showed a very less ohmic resistance of 0.00076 mΩ/cm².     

Electrochemically synthesized Cu/Pt core-shell catalysts on a porous carbon electrode for polymer electrolyte membrane fuel cells

A novel two-step method has been developed to efficiently prepare Cu/Pt core-shell structured catalysts for the first time. The Cu is first electrodeposited on the surface of the porous carbon electrode (PCE) and the deposited Cu is then partially replaced by Pt spontaneously. The addition of the thiourea (TU) along with the pH adjustment can tremendously reduce the self-dissolution of Cu due to dissolved oxygen. The results show that Cu/Pt core-shell structured catalysts display very good activities even at very low Pt loadings. The peak power density of a single cell using Cu/Pt core-shell structured catalysts is over 0.9 W cm⁻² at Pt loadings as low as 0.24 mg cm⁻² on each cathode and anode. This study shows that it is possible to apply this method for fabrication various core-shell structured functional materials.     

Pt/3D-graphene/FTO electrodes: Electrochemical preparation and their enhanced electrocatalytic activity

We report a facile, low-cost and green route to fabricate platinum nanoparticle (Pt NP) decorated three-dimensional (3D) graphene assembled on fluorine-doped tin oxide (FTO) electrodes (Pt/3D-G/FTO) with enhanced electrocatalytic activity. The fabrication process was accomplished by preparation of 3D graphene (3D-G/FTO) electrodes through electrochemical reduction of a graphene oxide suspension followed by electrodeposition of Pt NPs onto them. The Pt/3D-G/FTO electrode exhibits much higher catalytic activity and better stability for methanol oxidation compared with the electrodes prepared by electrodeposition of Pt NPs onto two-dimensional graphene sheets substrate (Pt/G/FTO) or bare FTO (Pt/FTO) under the same condition. These enhancements can be attributed to the high surface area, large void volume and high electrical conductivity as well as smaller size of Pt NPs in the hollows of the 3D architecture and a large amount of ridges on it.     

Mitigation studies of sulfur contaminated electrodes for PEMFC

The performance of Polymer Electrolyte Membrane Fuel Cell (PEMFC) is highly influenced by the contaminants present in the air, like sulfur compounds, nitrogen compounds, carbon oxides, chlorides etc. In particular, sulfur dioxide (SO₂) on the cathode side has a severe effect on the performance of PEMFC. In the present paper we have attempted to mitigate the effect of SO₂ poisoned catalyst layer of the fuel cell for both half cell and for single cell using a novel catalyst support. The mitigation strategies for the contaminated MEAs were studied by three different methods viz., electrochemical cycling, increased air stoichiometry and by successive polarization. The platinum on graphene as a catalyst support was found to have a better tolerance towards SO₂ contamination when compared with the conventional platinum supported on Vulcan XC carbon catalyst. Electrochemical and single cell contamination tests were done to study the extent of SO₂ poisoning on both the catalysts. The sulfur coverage was found to be less for Pt/G based catalyst, around 54% compared with Pt/C. The recovery by successive polarization was found to be better compared to air flow regulation. This may be attributed to the indirect removal of sulfur ions from Pt through scavenged OH⁻ ions.     

Comparative analysis of the electroactive area of Pt/C PEMFC electrodes in liquid and solid polymer contact by underpotential hydrogen adsorption/desorption

Because of the different experimental conditions found in literature for the measurement of the electroactive area of Pt/C electrodes of proton exchange membrane fuel cells (PEMFC) by means of underpotential hydrogen adsorption (H_UPD) voltammetry, specially concerning sweep rate and temperature, it was found necessary to perform an analysis of these parameters. With this aim, the electroactive area of PEMFC electrodes has been measured by means of H_UPD voltammetry at different sweep rates and temperatures, in liquid electrolyte and solid polymer contact. Both configurations show that H_UPD adsorption and desorption charges are strongly dependent on sweep rate voltage and temperature. The most common behaviour observed is a maximum in H_UPD desorption charge, typically in the 100–10 mV s⁻¹ sweep rate range, whereas H_UPD adsorption charge shows continuous increase with decreasing sweep rate. The decrease of desorption charge at low sweep rates is attributed to adsorbing species related with carbon support reactivity. These processes are also responsible for the increase in desorption H_UPD charge at low sweep rate. At high sweep rate, both adsorption and desorption H_UPD charges decrease due to limiting diffusion of protons through the microporous electrode. As a consequence, it is found that the closest approximation to the real electroactive area (i.e. the area accessible to protons) corresponds to the maximum in the H_UPD desorption charge in the range of 10–100 mV s⁻¹ sweep rate. The influence of measuring temperature is also tested in the range 25 °C–80 °C. A dependence of the adsorption and desorption hydrogen charges is found, due to thermodynamic and kinetics factors. We observe that the processes competing with hydrogen adsorption, i.e. generation and adsorption of carbon species are enhanced with temperature, so a low measuring temperature is found as most appropriate.     

Pt electrodeposited on CeZrO4/MCNT as a new alternative catalyst for enhancement of ethanol oxidation

Electrocatalytic preparation of Pt-based nanocomposites has been investigated for improvement of direct ethanol fuel cells (DEFCs). In this study, new alternative catalysts of Pt-decorated cerium zirconium oxide-modified multiwalled carbon nanotubes (Pt/CeZrO₄/MCNT) were successively prepared to improve the activity of the ethanol oxidation reaction (EOR). The prepared CeZrO₄ with a face-centered cubic (fcc) structure compatibly dispersed onto MCNT provides abundant active Pt sites for highly active catalysts. The fcc-structured Pt was also satisfactorily decorated onto CeZrO₄/MCNT, resulting in highly active Pt. The Ce⁴⁺/Ce³⁺ redox property can promote oxygen vacancies to improve the electrochemical activity for oxidation of carbonaceous species. An increase in roughness and a stabilized catalyst structure can also be produced by inserting Zr⁴⁺ into the ceria metal oxide. The prepared Pt/20%CeZrO₄/MCNT catalysts present excellent electrochemical active surface area, mass activity, CO tolerance and high electron kinetic transfer with low resistance and high stability over commercial PtRu/C toward EOR. This promising catalyst material could be introduced to enhance the anodic oxidation reaction in DEFCs.     

Effect of the deposition time on the electrocatalytic activity of Pt/C catalyst electrodes prepared by pulsed electrophoresis deposition method

Pt/C electrodes are prepared by pulsed electrophoresis deposition (PED) from a Pt colloidal solution as a plating bath. The PED is optimized by varying the duty cycle and deposition time in a galvanostatic mode. The catalytic activities of the Pt/C electrodes are evaluated using the cyclic voltammetry technique. The loading amount of the Pt catalyst is controlled by varying the deposition time. Also, a single cell test is carried out using the Pt/C electrodes prepared with the PED method as a cathode. In the concentration polarization region (i.e., at 0.4 V), the current density for the Pt/C 10 min electrode is 0.845 A cm⁻², which is higher than the rest of the Pt/C electrodes.     

Synthesis of well-dispersed Pt/carbon nanotubes catalyst using dimethylformamide as a cross-link

In synthesizing carbon nanotubes supported catalysts, a significant challenge is how to deposit metal nanoparticles uniformly on the surface of carbon nanotubes due to the inherent inertness of carbon nanotube walls. This study reports a facile procedure using N,N-dimethylformamide as a dispersant, ligand and reductant, with which Pt nanoparticles can be deposited uniformly on pristine carbon nanotubes. X-ray photoelectron spectroscopy measurements reveal that metallic Pt nanoparticles are successfully prepared with this method. Transmission electron microscopy and X-ray diffraction analyses confirm the formation of face-centered cubic crystal Pt particles with a size that ranges from 2.0 to 4.0 nm. The support-dependent catalytic properties of the prepared Pt catalyst are characterized by cyclic voltammetric studies of the formic acid electro-oxidation reaction. The results show that a pristine carbon nanotubes supported Pt catalyst has a higher catalytic activity than both carbon powder and modified carbon nanotubes supported catalysts.     

Electrochemical quartz crystal microbalance study of the electrodeposition of Co,Pt and Pt–Co alloy

The electrochemical deposition of Co, Pt and Pt–Co alloy are studied with the electrochemical quartz crystal microbalance (EQCM) on a gold substrate. Co is deposited from acidic sulphate bath containing boric acid. Different processes are identified in this bath. Electrodeposition of Co on Au substrate is observed at potentials above redox potential, underpotential deposition, most probably due to formation of a Co–Au alloy. At more cathodic potentials, below −0.5 V, metallic Co is formed. The film is completely dissolved at positive potentials during the anodic scan, probably mediated by Co(OH)₂. The electrodeposition of platinum from acidic PtCl₆²⁻ bath occurs below the thermodynamic potential (0.74 V) with almost 100% efficiency. At potentials negative from 0.0 V the efficiency decreases due to parallel water reduction. The codeposition of Co and Pt is also studied in acidic bath. Here, the decrease of pH due to water reduction on Pt deposits gives rise to precipitation of Co(OH)₂, together with the deposition of metallic Pt and Co. The films contain as major component the Pt₃Co alloy.     

Development of a novel portable-size PEMFC short stack with electrodeposited Pt hydrogen diffusion anodes

This paper presents, for the first time, a five-cell polymer electrolyte membrane fuel cell (PEMFC) short stack with electrodeposited hydrogen diffusion anodes. The anodes were manufactured by means of galvanostatic pulse electrodeposition and the cathodes by air-brushing. Nafion^® 212 was employed as a solid polymer electrolyte membrane in all cases. The short stack, whose cells had an active geometric area of 14 cm², was assembled and tested under different operating conditions. A peak power of about 11 W was obtained at 50 °C and atmospheric pressure using hydrogen and air feed, whereas a smaller value of 8.6 W was obtained from a five-cell short PEMFC stack with conventional hydrogen diffusion anodes under the same operating conditions. The better performance of the cells described in this paper has been assigned to the higher utilization of the platinum in the electrodeposited anodes compared to the conventional ones.     

Electrodeposition of PEM fuel cell catalysts by the use of a hydrogen depolarized anode

Up to 30% of the expensive catalyst metal in conventional fuel cell catalysts is not utilized in fuel cells caused by an absence of contact to either the ion conducting, electron conducting or educt phase. This contact can be improved by in situ electrodeposition with a precursor layer which is mostly done in a galvanostatic mode in the literature. In this paper electrochemical deposition with a hydrogen depolarized anode is described and so a potentiostatic electrodeposition under the control of the working-electrode potential and dry working-electrode conditions is enabled. This potentiostatic electrodeposition with a hydrogen depolarized anode significantly increases the performance of the fuel cell.     

One-pot synthesis of Pt/CeO2/C catalyst for improving the ORR activity and durability of PEMFC

Oxygen reduction reaction (ORR) activity and durability of Pt catalysts should be both valued for successful commercialization of proton exchange membrane fuel cells (PEMFCs). We offer a facile one-pot synthesis method to prepare Pt/CeO₂/C composite catalysts. CeO₂ nanoparticles, with high Ce³⁺ concentration ranging from 30.9% to 50.6%, offers the very defective surface where Pt nanoparticles preferentially nuclear and growth. The Pt nanoparticles are observed sitting on the CeO₂ surface, increasing the PtCeO₂ interface. The high concentration of oxygen vacancies on CeO₂ surface and large PtCeO₂ interface lead to the strong PtCeO₂ interaction, effectively improving the ORR activity and durability. The mass activity is increased by up to 50%, from 36.44 mA mg^?1 of Pt/C to 52.09 mA mg^?1 of Pt/CeO₂/C containing 20 wt.% CeO₂. Pt/CeO₂/C composite catalysts containing 10–30 wt.% CeO₂ loss about 80% electrochemical surface area after 10,000 cycles, which is a fivefold enhancement in durability, compared to Pt/C losing 79% electrochemical surface area after 2000 cycles.     

C16MI.OTf ionic liquid on Pt/C and PtMo/C anodes improves the PEMFC performance

The effect of 1-hexadecyl-3-methylimidazolium trifluoromethanesulfonate (C₁₆MI.OTf) ionic liquid (IL) on the catalytic activity of Pt/C or PtMo/C anodes is studied in a proton exchange membrane fuel cell (PEMFC). PtMo nanoparticles (NPs) are synthesized with two different Pt:Mo proportions (13 or 31 at.% Mo) by a borohydride method on the carbon support. The composition, crystalline structure, morphology of the PtMo/C are evaluated by energy-dispersive X-ray spectroscopy, X-ray diffraction and transmission electron microscopy, respectively. The stability tests of the electrocatalysts are carried out in acid medium using cyclic voltammetry measurements. Pt/C or PtMo/C electrocatalysts containing C₁₆MI.OTf are assessed in the anode in a H₂/air PEMFC by polarization curve and ac electrochemical impedance spectroscopy. The synthesized PtMo nanoparticles show spherical shape and average particle size of 3.5 nm. The PEMFC performance of PtMo (13 at.% Mo) at anode is very similar than of Pt/C anode. The presence of 15 wt% C₁₆MI.OTf in the Pt/C or PtMo/C (13 at.% Mo) anodes let to an increase of the maximum power values, 71 and 107 W g_Pt^?1 cm^?2, respectively. The catalytic surfaces of nanoparticles are modified due to C₁₆MI.OTf presence which improved the PEMFC performance. This result agrees with the EIS analysis, where the resistances of charge transfer and mass transfer decrease in the C₁₆MI.OTf presence. However, this effect is more pronounced for PtMo/C (13 at.% Mo) catalyst, demonstrate that PtMo/C anodes with a small amount of Mo and C₁₆MI.OTf ionic liquid improve significantly the PEMFC performance.     

Regeneration of CO poisoned Pt black anode catalyst in PEMFC using break-in procedure and KMnO4 solution

In the present work, an experimental procedure is developed based on break-in procedure and use of dilute KMnO₄ solution to regenerate the CO poisoned Pt black anode electro-catalyst of a PEMFC. To understand the effect of operating temperature on extent of CO poisoning and regeneration of CO poisoned Pt black anode electro-catalyst, PEMFC is operated at 30 °C, 50 °C and 70 °C. At lower cell operating temperature (30 °C), KMnO₄ solution regenerates CO poisoned Pt black anode catalyst, whereas contribution of break-in procedure towards regeneration is negligible. At 50 °C and 70 °C, break-in procedure contributes towards recovering the initial performance i.e. 74.6% and 78.8% of the initial current density at 0.2 V respectively and rest is regenerated by use of dilute KMnO₄ solution.     

Pulse electrodeposited cathode catalyst layers for PEM fuel cells

Nanostructured Pt and Pt₃Co cathodes for proton exchange membrane fuel cells (PEMFCs) have been prepared by pulse electrodeposition. For high utilization the catalyst nanoparticles are directly deposited on the microporous layer (MPL) of a commercial available gas diffusion layer (GDL). In order to increase the hydrophilic nature of the substrate surface and thus improve drastically the electrodeposition process and the fuel cell performance, prior to electrodeposition, the carbon substrate is submitted to O₂/Ar plasma activation. Cathodes with different amounts and distributions of Aquivion ionomer within the cathode catalyst layer (CCL) thickness (“homogeneous”, “gradient” and “anti-gradient”), different catalysts (Pt and Pt₃Co) at varied plasma duration and catalyst loading have been prepared. The cathodes are analysed via attenuated total reflection (ATR-IR), goniometer, SEM, 0.5 M H₂SO₄ half-cell and 25 cm² H₂/Air single PEMFC. The highest single fuel cell performance is obtained for 2 min plasma activated Pt₃Co cathode.     

Cathode catalyst layer using supported Pt catalyst on ordered mesoporous carbon for direct methanol fuel cell

The development of a cathode catalyst layer based on a supported Pt catalyst using an ordered mesoporous carbon (OMC) for direct methanol fuel cell is reported. An OMC with a mesopore structure between hexagonally arranged carbon nanorods is prepared using a template method. Platinum nanoparticles are supported on the OMC (Pt/OMC) with high metal loading of 60 wt.%. Compositional and morphological variations are made by varying the ionomer content and by compressing the catalyst layer to detect a parameter that determines the power performance. Increase in power density with decrease in the volume fraction of ionomer in the agglomerate comprising the Pt/OMC and the ionomer indicates that mass transport through the ionomer phase governs the kinetics of oxygen reduction. Impedance spectroscopic analysis suggests that a significant mass-transport limitation occurs at high ionomer content and in the compressed cathode. The power density of the optimum cathode layer, which employs a Pt/OMC catalyst with a Pt loading of 2 mg cm⁻², is greater than that of a catalyst layer with 6 mg cm⁻² Pt-black catalyst at a voltage higher than 0.4 V. This would lead to a significant reduction in the cost of the membrane electrode assembly.     

Analysis of electrocatalyst degradation in PEMFC caused by cell reversal during fuel starvation

The damage caused by cell reversal during proton exchange membrane fuel cell (PEMFC) operation with fuel starvation was investigated by a single cell experiment. The samples from degraded membrane–electrode assemblies (MEAs) were characterized. Chemical analysis of the anode catalyst layer of MEA samples by energy dispersive X-ray analysis (EDX) clearly showed ruthenium dissolution from the anode catalyst particles. Severe ruthenium loss was observed especially in the fuel outlet region. A reduced carbon monoxide (CO) tolerance was found by CO stripping voltammetry and measurement of deteriorated the fuel cell performance. Surface area loss of the cathode platinum by sintering was also detected by transmission electron microscopy (TEM) analysis and cyclic voltammetry.