Mesoporous carbon as Pt support for PEM fuel cell

A mesoporous carbon (MP) supported Pt nanocatalyst was evaluated as anode and cathode catalyst for PEM fuel cell. Kinetics study of the oxygen reduction reaction were characterized by using the rotating disk electrode (RDE) and rotating ring disk electrode (RRDE) techniques in acid media. Membrane electrode assemblies (MEAs) were prepared using Pt supported on MP as anodic and cathodic catalysts and the fuel cell performance evaluated. Polarization and power curves show a similar performance as cathode catalyst when compared to commercial catalyst while there is an 8% improvement when used as anode catalyst.     

Nitrogen doped mesoporous carbon supported Pt electrocatalyst for oxygen reduction reaction in proton exchange membrane fuel cells

Nitrogen doped mesoporous carbons are employed as supports for efficient electrocatalysts for oxygen reduction reaction. Heteroatom doped carbons favour the adsorption and reduction of molecular oxygen on Pt sites. In the present work, nitrogen doped mesoporous carbons (NMCs) with variable nitrogen content were synthesized via colloidal silica assisted sol-gel process with Ludox-AS40 (40 wt% SiO₂) as hard template using melamine and phenol as nitrogen and carbon precursors, respectively. The NMC were used as supports to prepare Pt/NMC electrocatalysts. The physicochemical properties of these materials were studied by SEM, TEM, XRD, BET, TGA, Raman, XPS and FTIR. The surface areas of 11 wt% (NMC-1) and 6 wt% (NMC-2) nitrogen doped mesoporous carbons are 609 m² g^?1 and 736 m² g^?1, respectively. The estimated electrochemical surface areas for Pt/NMC-1 and Pt/NMC-2 are 73 m² g^?1 and 59 m² g^?1, respectively. It is found that Pt/NMC-1 has higher ORR activity with higher limiting current and 44 mV positive onset potential shift compared to Pt/NMC-2. Further, the fuel cell assembled with Pt/NMC-1 as cathode catalyst delivered 1.8 times higher power density than Pt/NMC-2. It is proposed that higher nitrogen content and large pyridinic nitrogen sites present in NMC-1 support are responsible for higher ORR activity of Pt/NMC-1 and high power density of the fuel cell using Pt/NMC-1 cathode electrocatalyst. The carbon support material with high pyridinic content promotes the Pt dispersion with particle size less than 2 nm.     

Supported PtRu on mesoporous carbons for direct methanol fuel cells

We prepared and characterized several cryogel mesoporous carbons of different pore size distribution and report the catalytic activity of PtRu supported on mesoporous carbons of pore size >15 nm in passive and in active direct methanol fuel cells (DMFCs). At room temperature (RT), the specific maximum power of the passive DMFCs with mesoporous carbon/PtRu systems as anode was in the range 3–5 W g⁻¹. Passive DMFC assembly and RT tests limit the performance of the electrocatalytic systems and the anodes were thus tested in active DMFCs at 30, 60 and 80 °C. Their responses were also compared to those of commercial Vulcan carbon/PtRu. At 80 °C, the specific maximum power of the active DMFC with C656/PtRu was 37 W g⁻¹ and the required amount of Pt per kW estimated at 0.4 V cell voltage was 31 g kW⁻¹, a value less than half that of Vulcan carbon/PtRu.     

PtCo@NCNTs cathode catalyst using ZIF-67 for proton exchange membrane fuel cell

Zeolitic Imidazolate Frameworks (ZIF) is one of the potential candidates as highly conducting networks with large surface area with a possibility to be used as catalyst support for low temperature fuel cells. In the present study, highly active state-of-the-art PtCo@NCNTs (Nitrogen Doped Carbon Nanotube) catalyst was synthesized by pyrolyzing ZIF-67 along with Pt precursor under flowing ArH₂ atmosphere. The multi-walled NCNTs were densely grown on the surface of ZIF particles after pyrolysis. The high resolution TEM examination was employed to examine the nature of the PtCo particles as well as multi-walled NCNTs. Rotating disk electrode study was used for measuring oxygen reduction reaction performance for PtCo@NCNTs in 0.1 M HClO₄ and compared with commercial Pt/C catalyst. Fuel cell performance with PtCo@NCNT and commercial Pt/C catalysts was evaluated at 70 °C using Nafion-212 electrolyte using H₂ and O₂ gases (100% RH) and the observed peak power density of 630 and 560 mW cm^?2, respectively.     

Mechanically activated Pt–Ni and Pt–Co alloys as electrocatalysts in the oxygen reduction reaction

Mixtures of powders of platinum with nickel or cobalt to obtain Ni_0.75Pt_0.25 or Co_0.75Pt_0.25 were mechanical alloyed by high energy ball milling. The results of crystal structure, morphology and electrocatalytic performance are presented for mechanically activated powders after 3 and 9 h of ball milling. Total solid solutions of Ni and Co with platinum were analyzed by X-ray diffraction after 3 h of ball milling. After 9 h of ball milling, in both cases, the total solid solution was accompanied by the appearance of NiO or CoO and ZrO associated with a redox reaction with the milling media. The presence of zirconium monoxide was confirmed by energy dispersive spectroscopy analysis. In both cases, an amorphization was detected. X ray absorption spectroscopy measurements showed changes in atomic and electronic environment of platinum, a reduction of the distance to the first coordination sphere and increased d-band vacancy vs pure Pt and Pt nanoparticles were observed for both studied systems. The electrocatalytic activity was determined using cyclic and linear voltammetry. The Co_0.75Pt_0.25 alloy milled for 9 h showed a higher electrochemical activity for the oxygen reduction reaction (ORR) compared with the other samples, including Pt-Etek. The degree of the ORR electrochemical activity was correlated with the presence of ZrO, which could affect the oxygen adsorption and improve the catalytic activity for the oxygen reduction reaction.     

Polyethylene oxide-polypropylene oxide -polyethylene oxide derived porous carbon materials with different molecular weights as ORR catalyst in alkaline electrolytes

Polyethylene oxide (PEO)-polypropylene oxide (PPO)-polyethylene oxide block copolymer having different molecular weights are used as precursors of carbon materials to prepare Hollow -Derivatives carbon material as an electrocatalyst through block copolymer self-assembly. The composition and microstructure of the prepared catalysts are shown by Raman spectroscopy, X-ray diffraction (XRD), Test of nitrogen adsorption and desorption curves, High resolution transmission electron microscopy (HR-TEM) and scanning electron microscopy (HR-SEM). Oxygen was passed into alkaline electrolyte solution until the solution reached saturation state. With molecular weight increasing, the obtained sample gradually changed from block to hollow and spherical. When the molecular weight was 12600 g mol^?1, the evenly hollow carbon nanocages was acquired (C-12600). In O₂ saturated alkaline electrolyte (0.1 M KOH solution), C-12600's limited current density,half-wave potential and initial potential are 5.23 mA cm^?2@0.4 V, 0.72 V and 0.81 V, respectively. And most important is that half-wave potential and onset potential have barely change after 2000 cycles of cyclic voltammetry. As a result, the porous carbon materials exhibited excellent electrocatalytic activity while maintaining high stability in alkaline KOH solution.     

Pyrolyzed CoN4-chelate as an electrocatalyst for oxygen reduction reaction in acid media

A novel platinum-free electrocatalyst CoTETA/C for oxygen reduction reaction (ORR) was prepared from pyrolysis of carbon-supported cobalt triethylenetetramine chelate under an inert atmosphere. X-ray diffraction (XRD) measurement showed that nanometallic face-centered cubic (fcc) crystalline α-Co phase embedded in graphitic carbon was present on the pore surface of this catalyst. Cyclic voltammogram experiment showed that the ORR peak potential appears at 710 mV (vs. NHE) in oxygen-saturated acidic media (0.5 M H₂SO₄). The Koutecky–Levich analysis indicated that the ORR follows the first-order kinetic reaction and the ORR proceeds via both the two-electron reduction and the four-electron reduction, while the latter is the main process. The actual performance of a single cell with the obtained CoTETA/C electrocatalyst was examined under a hydrogen-oxygen fuel cell system, and the maximal output power density reached 135 mW cm⁻² at 25 °C.     

Facile preparing composite of CoSe2 wrapping N-doped mesoporous carbon with highly electrocatalytic activity for hydrogen evolution reaction

The composites of cobalt selenide (CoSe₂) wrapping nitrogen self-doped mesoporous graphitic carbon were facilely prepared by hydrothermally wrapping CoSe₂ on the carbon material derived from pyrolysis of N-containing zeolitic imidazolate framework. The composites exhibit excellent catalytic activities and durability for electrochemical hydrogen evolution reaction (HER) in 0.5 M H₂SO₄. The optimum composite catalyst needs only low overpotential of 159 mV to approach 10 mA/cm² and as low as 83 mV/dec of Tafel slope can be obtained. The results are among the most active for HER based on non-noble materials in acidic solution.     

Novel mesoporous carbon ceramics composites as electrodes for direct methanol fuel cell

In this work, a new family of materials for electrodes of direct methanol fuel cell (DMFC) is presented. Mesoporous carbon ceramics (MCCs) are obtained by the addition of commercial graphite into the synthesis gel of SBA-15 mesoporous silica with SiO₂/C weight ratios of 1/1 and 1/3. X-ray diffraction confirms both the formation of organized silica and the presence of graphite, and nitrogen physisorption measurements show that the presence of a graphitic phase does not interfere in the silica pore diameter although it diminishes the surface area. The MCCs modified with Pt or PtRu are tested as DMFC electrodes and compared with the commercial support Vulcan XC-72R. When used as cathode, the system using MCC-SBA-15 with SiO₂/C weight ratios of 1/1 presents a negligible performance, while the MCC-SBA-15 with SiO₂/C weight ratios of 1/3 is 2.9 times less active than the commercial support. On the other side, when used as anode, the MCC-SBA-15 with SiO₂/C weight ratios of 1/3 displays performances comparable to Vulcan XC-72R.     

Metal–organic framework derived CoS2/FeS-MOF with abundant heterogeneous interface as bifunctional electrocatalyst for electrolysis of water

Highly active and stable non-precious metal dual-functional electrocatalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are very important for the industrialization of water electrolysis. Herein, a three-dimensional (3D) porous CoS₂/FeS-MOF with adjustable Co/Fe molar ratio are in-stiu grown on a nickel foam (NF) to get a binder-free electrocatalyst electrode for HER and OER (CoS₂/FeS-MOF@NF). It should be emphasized that the MOFs precursor forms abundant heterogeneous interfaces through in-situ sulfidation. Moreover, the open skeleton and ordered porous structure of MOFs will not be destroyed due to the low temperature. The redistribution of electrons at the heterogeneous interfaces will produce more catalytic active centers, providing more active sites for reactant molecules or intermediates, thus availably promoting the electrocatalytic activity of the composite. Therefore, the optimized catalyst CoS₂/FeS-MOF@NF-1 displays high OER activity. The overpotential is only 136 mV at 10 mA cm^?2. At the same time, the CoS₂/FeS-MOF@NF-1 also shows good HER catalytic activity. Therefore, the assembled corresponding symmetric electrolyzer CoS₂/FeS-MOF@NF-1||CoS₂/FeS-MOF@NF-1 achieves a low cell voltage of 1.5 V at 10 mA cm^?2 with long time stability for 24 h. This work provides a simple and convenient strategy for the synthesis of transition metal sulfides dual-function electrocatalysts.