Highly dispersed platinum nanoparticles on graphitic carbon nitride: A highly active and durable electrocatalyst for oxidation of methanol,formic acid and formaldehyde

Finding efficient electrocatalyst for oxidation of small organic molecules such as methanol (CH₃OH), formic acid (HCOOH), formaldehyde (HCHO) etc. is essential for the development of their respective direct fuel cells. We report here highly dispersed platinum nanoparticles (PtNPs) on carbon nitride (CN_x) were successfully synthesized by the ultrasound mediated sodium borohydride reduction of H₂PtCl₆ in presence of CN_x nanosheets. This platinum–carbon nitride (Pt/CN_x) composite exhibited superior electrocatalytic activity towards oxidation of CH₃OH, HCOOH and HCHO in acid media. The mass activity, onset potential, tolerance to carbon monoxide (CO) poisoning and long term durability for the catalytic oxidation of CH₃OH, HCOOH, HCHO on Pt/CN_x catalyst in acid media is much higher than that of commercial Pt/C catalyst. The mass activity of Pt/CN_x catalyst at ～0.64 V (forward scan) is 310 mA/mg_Pt which is 2.7 time higher than that of commercial Pt/C for methanol oxidation. The electrooxidation of HCOOH on Pt/CN_x occurs via dual mechanism with greatly enhanced oxidation through dehydrogenation pathway in comparison with commercial Pt/C. The mass activity on Pt/CN_x at 0.3 V (vs. NHE) is 25 times higher than that of Pt/C for oxidation of HCOOH. The superior catalytic activity and durability of this Pt/CN_x catalyst can be attributed to high dispersion of PtNPs and strong catalyst support interaction.     

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.     

Single cell study of electrodeposited cathodic electrodes based on Pt-WO3 for polymer electrolyte fuel cells

Cathodic electrodes based on electrodeposited Pt-WO₃ material for proton exchange membrane fuel cells (PEMFC) were studied in single cell configuration. Preparation of the electrodes was carried out by electrodeposition of Pt and WO₃ on commercial gas diffusion layer substrates (microporous carbon black layer on carbon cloth, ELAT E-TEK). The process of simultaneous electrodeposition of Pt and WO₃ is first analyzed from voltammetric curves. It is observed that the deposition of Pt is enhanced when WO₃ is present. Compositional analysis of the electrodes shows metallic platinum and WO₃ in variable proportions. The electrodeposited electrodes were characterized in single PEMFC. Membrane-electrode assemblies were prepared with Nafion^® 117 electrolyte membrane and a standard Pt/C anode. Pt-WO₃ electrodes showed enhanced stability and good response in single cell up to 1500 h. Performance degradation is attributed to a decrease in Pt electroactive area and increase of the internal resistance of the cell. These effects are possibly a consequence of the production of mobile tungsten species, like soluble WO₂ at high current demands and low cathode potentials.     

Atomic layer deposition assisted Pt-SnO2 hybrid catalysts on nitrogen-doped CNTs with enhanced electrocatalytic activities for low temperature fuel cells

Nitrogen doped carbon nanotubes (CN_x) of a high nitrogen concentration were synthesized directly on carbon paper as the skeleton of a 3D composite electrode. Ultra-fine SnO₂ nanoparticles about 1.5 nm were deposited on CN_x with atomic layer deposition (ALD) technique. Pt nanoparticles from 1.5 to 4 nm were deposited on CN_x/carbon paper and SnO₂/CN_x/carbon paper with ethylene glycol reduction method. Three dimensional Pt/CN_x/carbon paper and Pt-SnO₂/CN_x/carbon paper composite electrodes were obtained, respectively. They were characterized over oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR) for low temperature fuel cells. With similar sizes of Pt nanoparticles, the electrochemical surface area (ECSA) of Pt-SnO₂/CN_x/carbon paper is larger than that of Pt/CN_x/carbon paper. Pre-deposited SnO₂ nanoparticles promote the electrocatalytic activity of Pt toward ORR, carbon monoxide (CO) stripping and MOR. The underlying mechanisms for the enhanced activities are discussed.     

Pt nanoparticles sputter-deposited on TiO2/MWCNT composites prepared by atomic layer deposition: Improved electrocatalytic activity towards the oxygen reduction reaction and durability in acid media

Acid-treated multi-walled carbon nanotubes (MWCNTs) were decorated with TiO₂ using the atomic layer deposition (ALD) technique followed by uniform distribution of platinum nanoparticles (PtNPs) through magnetron sputtering. Surface analyses were performed by scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM) and X-ray photoelectron spectroscopy (XPS). Electrochemical decontamination and characterization of the Pt-TiO₂/MWCNT electrodes were carried out by CO stripping followed by cyclic voltammetry in acid media. The oxygen reduction reaction (ORR) was studied in O₂-saturated 0.05 M H₂SO₄ solution using the rotating disk electrode (RDE) method. Durability of the prepared catalysts was examined by repetitive potential cycling. Electrochemical data obtained was analyzed and compared to that of the commercial Pt/C catalyst. It was revealed that the Pt-TiO₂/MWCNT catalysts possess higher ORR activity and better durability as compared to that of the commercial Pt/C.     

Plasma-assisted Pt and Pt–Pd nano-particles deposition on carbon carriers for application in PEM electrochemical cells

Plasma-assisted deposition of platinum and platinum-palladium nano-particles at the surface of carbonaceous electronic carriers for application in proton-exchange membrane (PEM) electrochemical cells has been carried out using a conventional DC magnetron sputtering system. Different types of carrier have been used for that purpose: carbon powder (Vulcan XC-72), carbon nanotubes and carbon nano-fibers. The interest of initial chemical pretreatment or metallization of the electronic carrier to improve surface adhesion of catalyst nano-particles has been analyzed. Nanostructured catalytic powders thus obtained have been analyzed and characterized using TGA, SEM, TEM, XRD, XRF and cyclic voltammetry. The electrochemical performances of Pt/C and Pt–Pd/C electrodes have been measured in single-cell PEM fuel cell (PEMFC), water electrolyzer (PEMWE) and unitized regenerative fuel cell (URFC). Results show a high active surface area (up to 44 m² g⁻¹) and high electrochemical activity for a number of synthesized samples. A qualitative correlation has been established between sputtering parameters, type of carbon carrier and performances as electrocatalyst.     

Fabrication of TiN inverse opal structure and Pt nanoparticles by atomic layer deposition for proton exchange membrane fuel cell

A titanium nitride (TiN) inverse opal structure was fabricated on carbon paper as a support of Pt for application in proton exchange membrane fuel cell (PEMFC). Polystyrene spheres with different diameters were coated on carbon paper by spin coating in multilayers as a template. Titanium dioxide (TiO₂) thin film was then deposited on the template by atomic layer deposition (ALD). The TiN inverse opal structure was fabricated by direct nitridation of TiO₂ in flowing ammonia atmosphere at above 800 °C. Platinum nanoparticles were then deposited uniformly on TiN by ALD. The performances of PEMFC using Pt@TiN@carbon paper composite as electrodes were examined. The homemade electrodes showed at least 13 times higher platinum specific power density than commercial E-Tek electrodes.     

Durable ultra-low-platinum ionomer-free anode catalyst for hydrogen proton exchange membrane fuel cell

An ultra-low-platinum catalyst based on finely dispersed platinum (Pt) deposited on a highly porous complex microporous layer was investigated as a candidate of durable anode catalyst for hydrogen oxidation reaction (HOR) in proton exchange membrane fuel cells. Etching of teflonated and nitridized base carbon substrate in oxygen plasma and simultaneous deposition of cerium oxide were applied to increase active surface area and electrochemical activity of the platinum nanocatalyst. Ultra-low loadings of Pt (between 0.85 and 8.5 μg cm⁻²) deposited by magnetron sputtering on this substrate were assembled with Nafion 212 membrane and commercially available Pt/C cathodes (300-400 μg cm⁻² Pt). Such membrane electrode assembly (MEA) with extremely low Pt content at anode can deliver high output power densities, reaching 0.95 W cm⁻² or 0.65 W cm⁻² with only 1.7 μg cm⁻² of Pt, using H₂ as fuel and pure O₂ or air as an oxidant, respectively. Although electrocatalysts with highly dispersed active metals are known to often suffer from irreversible degradation, the above MEAs proved to be very stable when the cell was subjected to a durability test under heavy duty conditions of on/off cycling. The system with lower Pt content is more prone to water flooding which can, however, be eliminated by maintaining better control over the fuel humidity. Average decay of the cell voltage less than 50 μV h⁻¹ was obtained in the cycling regime, while excellent stability <10 μV h⁻¹ is achievable under the static load of 0.4 A cm⁻².     

Hydrogen generation from sodium borohydride hydrolysis by multi-walled carbon nanotube supported platinum catalyst: A kinetic study

In this study, it is aimed to investigate hydrogen (H₂) generation from sodium borohydride (NaBH₄) hydrolysis by multi-walled carbon nanotube supported platinum catalyst (Pt/MWCNT) under various conditions (0–0.03 g Pt amount catalyst, 2.58–5.03 wt % NaBH₄, and 27–67 °C) in detail. For comparison, carbon supported platinum (Pt/C) commercial catalyst was used for H₂ generation experiments under the same conditions. The reaction rate of the experiments was described by a power law model which depends on the temperature of the reaction and concentrations of NaBH₄. Kinetic studies of both Pt/MWCNT and Pt/C catalysts were done and activation energies, which is the required minimum energy to overcome the energy barrier, were found as 27 kJ/mol and 36 kJ/mol, respectively. Pt/MWCNT catalyst is accelerated the reaction less than Pt/C catalyst while Pt/MWCNT is more efficient than Pt/C catalyst, they are approximately 98% and 95%, respectively. According to the results of experiments and the kinetic study, the reaction system based on NaBH₄ in the presence of Pt/MWCNT catalyst can be a potential hydrogen generation system for portable applications of proton exchange membrane fuel cell (PEMFC).     

Tantalum nitride coated AISI 316L as bipolar plate for polymer electrolyte membrane fuel cell

Tantalum nitride (TaN) thin films are deposited on AISI 316L stainless steel by inductively coupled, plasma-assisted, reactive magnetron sputtering at various N₂ flow rates. TaN film behavior is investigated in simulated polymer electrolyte membrane fuel cell (PEMFC) conditions by using electrochemical measurement techniques for application as bipolar plates. The results of a potentio-dynamic polarization test under PEMFC cathodic and anodic conditions indicate that the corrosion current density of the TaN_x films is of the order of 10⁻⁷ A cm⁻² (at 0.6 V) and 10⁻⁸ A cm⁻² (at −0.1 V), respectively; these results are considerably better than the individual results for metallic Ta films and AISI 316L stainless steel. The TaN_x films exhibit superior stability in a potentio-static polarization test performed under PEMFC cathodic and anodic conditions. The interfacial contact resistance of the films is measured in the range of 50-150 N cm⁻², and the lowest value is 11 mΩ cm² at a compaction pressure of 150 N cm⁻².     

One-step fabrication of new generation graphene-based electrodes for polymer electrolyte membrane fuel cells by a novel electrophoretic deposition

High Pt loading has better tradeoff in polymer electrolyte membrane fuel cell (PEMFC) in terms of improved performance and operational longevity. But, to employ low amounts of Pt electrocatalysts via an alternative carbon-based support and utilization technique is vital. This study presents the use of a one-step novel technique, an electrophoretic deposition (EPD) method, through which reduced graphene oxide (rGO) supported Pt nanoparticles have been directly fabricated onto carbon paper to form electrodes for PEMFC. Our process involves simultaneous synthesis and deposition of Pt-reduced GO nanocomposites onto oxygen plasma pre-treated carbon paper in an organo-aqueous media at various deposition time. Through this technique, homogenously distributed Pt nanoparticles ranging from 5 to 6 nm in size on graphene support were successfully synthesized to form catalyst layer on carbon paper. The characteristics of fabricated electrodes were investigated ex-situ by Raman spectroscopy, FE-SEM, XPS, ICP, FIB, TEM. Furthermore, catalytic activity towards hydrogen oxidation reaction was evaluated via CV measurements and fuel cell performance tests were also conducted. The highest ECSA value of 27.4 m²g^-1 and the Pt utilization efficiency of 1.48 kW/g_Pt^?1 were achieved at an optimized Pt loading of 0.129 mg cm^?2. A maximum power density of 280 mW cm^?2 was obtained with increasing EPD time and Pt precursor concentration at the same time. The achieved results are attributed to the dispersion of Pt nanoparticles on rGO nanosheets displaying synergetic performance as catalyst necessary for PEMFCs, thanks to the EPD technique's viability, ease in handling, and reproducibility in the synthesis route. In the previous studies on Pt/GO based fuel cell electrodes by EPD, on one hand, Pt NPs were synthesized on GO by chemical methods first and electrodes were fabricated by a subsequent EPD. On the other hand, the fuel cell performances of those electrodes have been rarely shown. To the best of our knowledge, this is the first time in literature not only about the use of EPD technique for the fabrication of fuel cell electrodes in one-step but also the evaluation of fuel cell performance of the electrodes fabricated by EPD.     

Activity and durability of electrocatalytic layers with low platinum loading prepared by magnetron sputtering onto gas diffusion electrodes

This article presents development of magnetron sputtering technology for catalytic Pt coating production. Low Pt-loaded gas diffusion electrodes were prepared by a single-step magnetron sputtering in different regimes. Pt and Pt-carbon films (95–97 wt% Pt) were deposited directly onto the gas diffusion layers (GDLs): carbon paper (Sigracet® 39 BC) and carbon cloths (GDL-CT, ELAT® LT 1400 W). A bipolar pulsed direct current (DC) magnetron sputtering with pulsed frequency 100 kHz was used as the method for catalysts deposition. Total Pt loading in the thin films varied in the range 0.04–0.13 mg*cm⁻². Obtained catalysts onto GDLs were investigated by scanning/transmission electron microscope (S/TEM), X-ray Absorption Near Edge Structure (XANES) and potentiodynamic methods. The deposited catalysts had a high electrochemical surface area (ECSA) and stability determined by the durability stress test (DST) method. The highest ECSA was obtained with Pt target in the pulsed (100 kHz) sputtering mode. This ECSA values were rather stable during 3000 cycles of stress-tests versus 500 cycles for Pt deposited by polyol method on the same gas diffusion layers.     

Experimental validation of the “EasyTest Cell” operational principle for autonomous MEA characterization

The paper presents the experimental validation of the “EasyTest Cell” operational principle via comparative electrochemical tests on MEAs carried out in three types of electrochemical hydrogen energy conversion (EHEC) testing cells: conventional polymer electrolyte membrane fuel cells (PEMFC) and polymer electrolyte membrane water electrolyzers (PEMWE), properly equipped with all the required auxiliaries (products conditioning and supplying, reagents removal, etc.), and the simple, autonomous EasyTest Cell. Along with EasyTest Cell validation and demonstration of its advantages, the influence of argon pressure during sputtering on the electrode characteristics, including gas diffusion limitations was investigated. The electrodes under investigation were magnetron sputtered C/Ti/IrO_x (IrO_x loading in the range 0.12–0.4 mg cm⁻²), C/Ti/IrO_x/Pt/IrO_x (IrO_x 0.08/Pt 0.06/IrO_x 0.08 mg cm⁻²), sputtered at various argon pressure C/Ti/Pt (0.15 and 0.25 mg cm⁻²), and commercial ELAT electrode (V.21, Lot # MB030105-1, Pt loading 0.5 mg cm⁻², E-TEK). The results obtained proved the reliability, simplicity (running-periphery-free) and broadened experimental possibilities of EasyTest Cell over PEMFC and PEMWE single cell testing. Thus, significant cost reduction and resource saving in R&D laboratory can be achieved. Moreover, validation of EasyTest Cell contributes not only to testing facilitations, but potentially to standardization of MEA testing since it gives possibilities for precise control and more uniform distribution of the working parameters applied to the testing object, which are both compulsory for performance comparison and qualifying.     

Pt/C catalyst impregnated with tungsten-oxide – Hydrogen oxidation reaction vs. CO tolerance

Hydrogen Oxidation Reaction (HOR) is anode reaction in Proton exchange membrane fuel cells (PEMFCs) and it has very fast kinetics. However, the purity of fuel (H₂) is very important and can slow down HOR kinetics, affecting the overall PEMFC performance. The performance of commercial Pt/C catalyst impregnated with WO_x, as a catalyst for HOR, was investigated using a set of electrochemical methods (cyclic voltammetry, linear scan voltammetry and rotating disk electrode voltammetry). In order to deepen the understanding how WO_x species can contribute CO tolerance of Pt/C, a particular attention was paid to CO poisoning. In the absence of CO, HOR is under diffusion limitations and HOR kinetics is not affected by WO_x species. Appreciable HOR current on the electrodes pre-saturated with CO_ads at potentials above 0.3 V vs. RHE, which is not observed for pure Pt/C, was discussed in details. HOR liming diffusion currents for higher concentrations of W are reached at high anodic potentials. The obtained results were explained by donation of OH_ads by WO_x phase for CO_ads removal in the mid potential region and reduced reactivity of Pt surface sites in the vicinity of the Pt|WO_x interface. The obtained results can provide guidelines for development of novel CO tolerant PEMFC anode catalysts.     

Highly efficient and ORR active platinum-scandium alloy-partially exfoliated carbon nanotubes electrocatalyst for Proton Exchange Membrane Fuel Cell

Oxygen reduction reaction (ORR) in Proton Exchange Membrane Fuel Cell (PEMFC) is the most sluggish reaction, which impedes the performance and commercialization of PEMFC. Platinum-based alloys show higher ORR activity than Pt and it is suggested by density functional theory calculations that Pt₃Sc alloy has high stability and higher ORR activity due to filling the metal d-bands and lowers binding energy of the oxygen species respectively. Herein, we report Pt₃Sc alloy nanoparticles (NPs) dispersed over partially exfoliated carbon nanotubes (PECNTs) as a cathode catalyst for single-cell measurements of PEMFC where Pt₃Sc alloy shows a lower binding energy towards oxygen and facilitates ORR with much faster kinetics. The ORR activity of Pt₃Sc/PECNTs electrocatalyst, investigated by cyclic voltammetry, Rotating Disk electrode (RDE) and Rotating Ring Disk electrode (RRDE), shows the higher mass activity and lower H₂O₂ formation than the commercial catalyst Pt/C-TKK. Accelerated Durability Tests (ADT) was performed to evaluate the stability of catalysts in acidic medium. In single-cell measurements, Pt₃Sc/PECNTs cathode catalyst exhibits a power density of 760 mW cm⁻² at 60 °C. Our study gives an important insight into the design of a novel ORR electrocatalyst with an excellent stability and high power density of PEMFC.     

Investigation of tungsten carbide supported Pd or Pt as anode catalysts for PEM fuel cells

In this contribution, we present results of electrochemical characterization of prepared tungsten carbide supported palladium and platinum and Vulcan XC-72 supported palladium. These catalysts were employed as anode catalysts in PEMFC and results are compared to commercial platinum catalyst. Platinum seems to be irreplaceable as a proton exchange membrane fuel cell (PEMFC) catalyst for both the anode and the cathode, yet the high price and limited natural resources are holding back the commercialization of the PEMFCs. Tungsten carbide is recognized as promising catalyst support having the best conductivity among interstitial carbides. Higher natural resources and significantly lower price make palladium good candidate for replacement of the platinum catalyst. The presented results show that all prepared catalysts are very active for the hydrogen oxidation reaction. Linear sweep voltammetry curves of Pd/C and Pd/WC show existence of peaks at 0.07 V vs. RHE, which is assigned to absorbed hydrogen. H₂|Pd/WC|Nafion117|Pt/C|O₂ fuel cell has almost the same efficiency and similar power output as commercial platinum catalyst.     

A Nafion-based self-humidifying membrane with ordered dispersed Pt layer

A double-layer Nafion-based membrane consisting of a pure Nafion layer and an ordered dispersed Pt particles layer was investigated. The Pt particles were dispersed under the anode graphite ribs, which provide the sites for the recombination of the permeating _H2${\mathrm{H}}_2$ and _O2${\mathrm{O}}_2$ into water. The electrochemical performances of the ordered Pt particles dispersed membrane in proton exchange membrane fuel cell (PEMFC) were studied and compared with those of the common Pt particles dispersed membrane and the pure Nafion membrane. The results indicate that the ordered Pt dispersed membrane reduces the amount of Pt dosage than the common Pt dispersed membrane and improves the performance of PEMFC operated under dry conditions than the pure Nafion membrane as well.     

Non-platinum cathode catalysts for alkaline membrane fuel cells

Hydrogen–oxygen fuel cells using an alkaline anion exchange membrane were prepared and evaluated. Various non-platinum catalyst materials were investigated by fabricating membrane-electrode assemblies (MEAs) using Tokuyama membrane (# A201) and compared with commercial noble metal catalysts. Co and Fe phthalocyanine catalyst materials were synthesized using multi-walled carbon nanotubes (MWCNTs) as support materials. X-ray photoelectron spectroscopic study was conducted in order to examine the surface composition. The electroreduction of oxygen has been investigated on Fe phthalocyanine/MWCNT, Co phthalocyanine/MWCNT and commercial Pt/C catalysts. The oxygen reduction reaction kinetics on these catalyst materials were evaluated using rotating disk electrodes in 0.1 M KOH solution and the current density values were consistently higher for Co phthalocyanine based electrodes compared to Fe phthalocyanine. The fuel cell performance of the MEAs with Co and Fe phthalocyanines and Tanaka Kikinzoku Kogyo Pt/C cathode catalysts were 100, 60 and 120 mW cm⁻² using H₂ and O₂ gases.     

Non-noble metal oxygen reduction electrocatalysts based on carbon nanotubes with controlled nitrogen contents

Nitrogen-doped carbon nanotubes (CN_x) were prepared via a floating catalyst chemical vapor deposition method using precursors consisting of ferrocene and melamine to control the nitrogen content. Structure, morphology and composition of all CN_x catalysts were characterized by SEM, TEM, and XPS. These results indicated that the surface nitrogen content (up to 7.7 at.%) increases with the increase of melamine used. Electrochemical methods were used to study the correlation between surface structure and the activity of oxygen reduction reaction (ORR) in acid and alkaline solutions. Electrochemical data indicated that the higher the nitrogen content is, the higher the oxygen reduction activity. Especially, the results from the rotating ring disk electrode technique demonstrated that CN_x (7.7%) has similar ORR activity and selectivity with commercial Pt/C in alkaline solution.