The potential of novel carbon nanocages as a carbon support for an enhanced methanol electro-oxidation reaction in a direct methanol fuel cell

In this study, we introduce the potential for a new catalyst support, namely, carbon nanocages (CNCs) for anodic direct methanol fuel cell (DMFC). The synthesis, characterization and catalytic activities of four electrocatalysts, PtRu/CNC, PtNi/CNC, PtFe/CNC and PtCo/CNC, have been investigated. These electrocatalysts are synthesized using pyrolysis, followed by a microwave-assisted ethylene glycol reduction method. From X-ray diffraction analysis, PtNi/CNC and PtRu/CNC showed the smallest crystallite particle size of Pt-alloy, which corresponded to the (111) plane. The Raman spectra confirmed the presence of the carbon support material in all prepared electrocatalysts. The ratio value of the D band and G band (I_D/I_G) of all prepared samples was not much different within the electrocatalyst and CNC. The I_D/I_G values calculated for the CNC, PtNi/CNC, PtRu/CNC, PtCo/CNC and PtFe/CNC electrocatalysts were 0.90, 0.89, 0.83, 0.78 and 0.77, respectively. Therefore, the number of defects of graphitization in increasing order (I_D/I_G) was PtFe/CNC < PtCo/CNC < PtRu/CNC < PtNi/CNC < CNC. Brunauer-Emmett-Teller analysis revealed that the CNC support has a mesoporous-type structure with a high surface area of 416 m² g⁻¹, which indicates that this support has a high potential to act as an excellent catalyst support. From the cyclic voltammetry curve, PtRu/CNC showed the highest catalytic activity in methanol electro-oxidation and reached a value of 427 mA mg⁻¹, followed by PtNi/CNC (384.11 mA mg⁻¹), PtCo/CNC (150.53 mA mg⁻¹) and PtFe/CNC (144.11 mA mg⁻¹). PtFe/CNC exhibited a higher ratio value of I_f/I_b (3.24) compared with PtRu/CNC (2.34), PtNi/CNC (1.43) and PtCo/CNC (1.62). These values show that the combination of Pt and Fe catalysts in PtFe/CNC had better CO tolerance than PtRu/CNC, PtNi/CNC and PtCo/CNC electrocatalysts. The higher performance of PtRu/CNC was attributed to the fact that it had the smallest bimetallic-Pt crystallite; there was a smooth distribution of bimetallic-Pt on its CNC support, as shown by field emission scanning electron microscopy; it had the highest electrochemical surface area value (16.23 m² g⁻¹); and it had an overall catalytic performance enhanced by the advantages of the unique and large surface area from the CNC as support material. In passive DMFC mode, PtRu/CNC showed a maximum power density of 3.35 mW cm⁻², which is 1.72 times higher than that of the PtRu/C commercial electrocatalyst.     

Experimental investigation on DMFCs using reduced noble metal loading with NiTiO3 as supportive material to enhance cell performances

In this present work, the effect of anode electrocatalyst materials is investigated by adding NiTiO₃ with Pt/C and Pt-Ru/C for the performance enhancement of direct methanol fuel cells (DMFCs). The supportive material NiTiO₃/C has been synthesized first by wet chemical method followed by incorporation of Pt and Pt-Ru separately. Experiments are conducted with the combination of four different electrocatalyst materials on the anode side (Pt/C, Pt-NiTiO₃/C, PtRu/C, Pt-Ru-NiTiO₃/C) and with commercial 20 wt % Pt/C on the cathode side; 0.5 mg_pt/cm² loading is maintained on both sides. The performance tests of the above catalysts are conducted on 5 cm² active area with various operating conditions like cell operating temperatures, methanol/water molar concentrations and reactant flow rates. Best performing operating conditions have been optimized. The maximum peak power densities attained are 13.30 mW/cm² (26.6 mW/mg_pt) and 14.60 mW/cm² (29.2 mW/mg_pt) for Pt-NiTiO₃/C and Pt-Ru-NiTiO₃/C at 80 °C, respectively, with 0.5 M concentration of methanol and fuel flow rate of 3 ml/min (anode) and oxygen flow rate of 100 ml/min (cathode). Besides, 5 h short term stability tests have been conducted for PtRu/C and Pt-NiTiO₃/C. The overall results suggest that the incorporation of NiTiO₃/C supportive material to Pt and Pt-Ru appears to make a promising anode electrocatalysts for the enhanced DMFC performances.     

Preparation of a CO-tolerant PtRuxSny/C electrocatalyst with an optimal Ru/Sn ratio by selective Sn-deposition on the surfaces of Pt and Ru

A CO-tolerant PtRu_xSn_y/C electrocatalyst, with an optimal x/y ratio of 0.8/0.2, was prepared by selectively depositing Sn on the metallic surface of PtRu_0.8/C for use as the anode in a polymer electrolyte membrane fuel cell. The CO tolerance of the catalyst was greater when Sn was added by chemical vapor deposition (CVD) than by a conventional precipitation method because most of the Sn added by CVD was located in the vicinity of Pt and Ru surfaces, on which CO molecules were strongly adsorbed. Accordingly, the bi-functional mechanism of CO oxidation, which involved the migration of oxygenated species from the Sn to the adsorbed CO, was expected to be promoted to greater extents in the catalysts prepared by Sn-CVD than those prepared by Sn-precipitation. On the other hand, the ligand-effect mechanism of CO oxidation, which was facilitated by the Pt-Ru alloy formation, was not much affected by the added Sn because the Pt-Ru alloy remained unchanged, particularly when y ≤ 0.2. Among PtRu_xSn_y/C catalysts prepared by Sn-CVD, one prepared by partially substituting Sn for Ru in the PtRu_1.0/C catalyst, e.g., PtRu_0.8Sn_0.2/C, showed higher CO tolerance than one prepared by simply adding Sn to the PtRu_1.0/C catalyst, e.g., PtRu_1.0Sn_0.2/C, which demonstrated the importance of an optimum x/y ratio in the design of the ternary PtRu_xSn_y/C catalysts.     

Performance of direct methanol fuel cell using carbon nanotube-supported Pt–Ru anode catalyst with controlled composition

The performance of a single-cell direct methanol fuel cell (DMFC) using carbon nanotube-supported Pt–Ru (Pt–Ru/CNT) as an anode catalyst has been investigated. In this study, the Pt–Ru/CNT electrocatalyst was successfully synthesized using a modified polyol approach with a controlled composition very close to 20 wt.%Pt–10 wt.%Ru, and the anode was prepared by coating Pt–Ru/CNT electrocatalyst on a wet-proof carbon cloth substrate with a metal loading of about 4 mg cm⁻². A commercial gas diffusion electrode (GDE) with a platinum black loading of 4 mg cm⁻² obtained from E-TEK was employed as the cathode. The membrane electrode assembly (MEA) was fabricated using Nafion^® 117 membrane and the single-cell DMFC was assembled with graphite endplates as current collectors. Experiments were carried out at moderate low temperatures using 1 M CH₃OH aqueous solution and pure oxygen as reactants. Excellent cell performance was observed. The tested cell significantly outperformed a comparison cell using a commercial anode coated with carbon-supported Pt–Ru (Pt–Ru/C) electrocatalyst of similar composition and loading. High conductivity of carbon nanotube, good catalyst morphology and suitable catalyst composition of the prepared Pt–Ru/CNT electrocatalyst are considered to be some of the key factors leading to enhanced cell performance.     

The stability of a PtRu/C electrocatalyst at anode potentials in a direct methanol fuel cell

Potential-scan tests were conducted to evaluate the stability of a PtRu/C electrocatalyst at anode potentials in a direct methanol fuel cell (DMFC). The results show that, under normal operating conditions, the anode potential in a DMFC is benign for the PtRu/C electrocatalyst. But in the case of deep discharge or short circuit, the anode potential value may exceed 0.6 V versus DHE, which is harmful to the PtRu/C electrocatalyst. The dissolution of catalyst components results in an enhanced ohmic resistance and a lowered catalytic activity for methanol electro-oxidation.     

Improvement in stability of PtRu electrocatalyst by carbonization of in-situ polymerized polyaniline

As well known, ruthenium is electrochemically unstable in direct methanol fuel cell (DMFC) operation shortening lifetime and deteriorating performance of DMFC device. In this work, a facile methodology for improvement in stability of PtRu electrocatalyst is described, in which PtRu alloyed nanoparticles are decorated by nitrogen-doped carbon (N_xC) originating from the carburization of in-situ polymerized polyaniline (PANI). Deceleration in Ru dissolution of N_xC protected PtRu electrocatalyst comes from the ionized Ru atoms induced by the carburization of PANI transferring electrons from Ru to nitrogen atoms evidenced by XPS measurement, which results in higher CO tolerance during potential sweeping from 0.6 to 1.0 V versus RHE for N_xC decorated PtRu electrocatalyst. Meanwhile, N_xC protected PtRu electrocatalyst only losses 10% of active sites after stability estimation; in contrast, 50% of active sites are lost for bare PtRu electrocatalyst. Moreover, fuel cell test illustrates that N_xC protected PtRu electrocatalyst shows comparable performance to bare PtRu electrocatalyst.     

Maximized specific activity for the methanol electrooxidation by the optimized PtRu-TiO2-carbon nano-composite structure

The kinetics of the methanol electrooxidation needs to be improved to increase the power density using a lower amount of noble metal catalysts (i.e., Pt and Ru) in direct methanol fuel cells (DMFC). PtRu nanoparticles (∼5 nm) supported on TiO₂-nanoparticle (∼4 nm)-coated carbon nanofibers were proposed as an alternative active catalyst for the DMFC. The nano-sized TiO₂ can provide a short distance of electron transport from PtRu (reaction site) to the carbon (current collector). At the composite catalyst, the activity enhancement by the PtRu-TiO₂ interaction suggested the sufficient electron conductivity at the electrode. The maximized specific activity of the proposed catalyst was 3 times higher compared to that of the commercial PtRu/C. The pore structure of the catalyst was changed by the oxidation conditions due to gasification of the carbon, and the higher activity was obtained by the catalyst with the higher surface area of the micropores (>800 m² g⁻¹). However, the contribution of micropore would be a secondary effect to the activity. The maximized specific activity was obtained when the volumes of PtRu and TiO₂ were similar for the almost same size (around 5 nm) of these particles suggesting that the number of contact points between the PtRu and TiO₂ were optimized and the interaction between them was maximized. The PtRu-TiO₂-carbon nano-composite catalyst has a high potential as an alternative catalyst as the anode of DMFC.     

Optimization of process parameters using response surface methodology (RSM) for power generation via electrooxidation of glycerol in T-Shaped air breathing microfluidic fuel cell (MFC)

The present work focuses on the optimization of operating parameters using Box Behnken design (BBD) in RSM to obtain maximum power density from a glycerol based air-breathing T-shaped MFC. The major parameters influencing the experiment for enhancing the cell performance in MFC are glycerol/fuel concentration, anode electrolyte/KOH concentration, anode electrocatalyst loading and cathode electrolyte/KOH concentration. The ambient oxygen is used as the oxidant. The acetylene black carbon (C_AB) supported laboratory synthesized electrocatalyst Pd–Pt (16:4)/C_AB is used as anode electrocatalyst and commercial Pt (40 wt%)/C_HSA as the cathode electrocatalyst. The quadratic model predicts the appropriate operating conditions to achieve highest power density from the laboratory designed T-shaped MFC. The p-value of less than 0.0001 and F-value of greater than 1 i.e., 26.32 indicate that the model is significant. The optimum conditions predicted by the RSM model were glycerol concentration of 1.07 M, anode electrolyte concentration of 1.62 M anode electrocatalyst loading of 1.12 mg/cm² and cathode electrolyte concentration of 0.69 M. The negligible deviation of only 1.07% between actual/experimental power density (2.76 mW/cm²) and predicted power density (2.79 mW/cm²) was recorded. This model reasonably predicts the optimum conditions using Pd–Pt (16:4)/C_AB electrocatalyst to obtain maximum power density from glycerol based MFC.     

A novel electrocatalyst support with proton conductive properties for polymer electrolyte membrane fuel cell applications

The objective of this study is to graft the surface of carbon black, by chemically introducing polymeric chains (Nafion^® like) with proton-conducting properties. This procedure aims for a better interaction of the proton-conducting phase with the metallic catalyst particles, as well as hinders posterior support particle agglomeration. Also loss of active surface can be prevented. The proton conduction between the active electrocatalyst site and the Nafion^® ionomer membrane should be enhanced, thus diminishing the ohmic drop in the polymer electrolyte membrane fuel cell (PEMFC). PtRu nanoparticles were supported on different carbon materials by the impregnation method and direct reduction with ethylene glycol and characterized using amongst others FTIR, XRD and TEM. The screen printing technique was used to produce membrane electrode assemblies (MEA) for single cell tests in H₂/air (PEMFC) and methanol operation (DMFC). In the PEMFC experiments, PtRu supported on grafted carbon shows 550 mW cm⁻² gmetal⁻¹ power density, which represents at least 78% improvement in performance, compared to the power density of commercial PtRu/C ETEK. The DMFC results of the grafted electrocatalyst achieve around 100% improvement. The polarization curves results clearly show that the main cause of the observed effect is the reduction in ohmic drop, caused by the grafted polymer.     

A new durable and high performance platinum supported on Ag–Ni-porous coordination polymer as an anodic DMFC nano-electrocatalyst: DFT and experimental investigation

Due to the poor performance and intermediates poisoning of available catalysts in direct methanol fuel cells (DMFC), the researcher is confronted with a considerable challenge for obtaining modified electrocatalyst. Ag–Ni porous coordination polymer (ANP) as a new electrocatalyst supporter was synthesized by a hydrothermal method. To achieve favorable electrocatalyst for DMFC systems, platinum nanoparticles was deposited upon ANP by an electrochemical method and platinum supported on Ag–Ni porous coordination polymer (Pt-ANP) was formed. Fourier transform infrared spectroscopy (FTIR) analysis ensured correct synthesized of ANP and Pt-ANP. In addition, the morphologies investigation of ANP and Pt-ANP were carried out by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM). The FE-SEM images indicate that the platinum nanoparticles have been greatly deposited on ANP surface. Electrochemical behaviors of prepared catalyst for methanol oxidation were evaluated by cyclic voltammetry (CV), linear sweep voltammetry (LSV), and chronoamperometry (CA) techniques. Electrochemical cyclic voltammetry tests (CV) indicate that the forward peak current density of Pt-ANP is about 105 mA/cm² which it is 33% more than the forward peak current density of pure Pt catalyst (70.21 mA/cm²). Moreover, electrochemical surface area (ECSA) of Pt-ANP is 26.42 m²/g_Pt. In addition, density functional theory (DFT) computations show that with the deposition of Pt upon ANP, the HOMO-LOMO energy gap of ANP has been decreased which they are suitable for electrochemical reactions. Theoretical results are greatly in accordance with the experiments. Based on the results, Pt-ANP could be a superior electrocatalyst for methanol oxidation.     

A study on composite PtRu(1:1)-PtSn(3:1) anode catalyst for PEMFC

Composite PtRu(1:1)/C-PtSn(3:1)/C catalyst layers with various geometries and loadings were designed for a proton exchange membrane fuel cell (PEMFC) anode to improve carbon monoxide (CO) tolerance of the conventional PtRu(1:1)/C catalyst. The idea was based on an experimental finding that the onset potential of the PtSn for CO oxidation was lower than that of the PtRu and the resultant expectation that there seemed to be a possibility of using the PtSn as a CO filter. The CO tolerance of the composite catalyst of each design was judged by the cell performance obtained through a single cell test using H₂/CO gases of various CO concentrations and compared to that of the PtRu/C catalyst. The highest CO tolerance among the composite catalysts tested in this study was obtained for the one with geometry of double layers in the order of PtRu/C and PtSn/C from the electrolyte layer and with respective PtRu and PtSn loadings of 0.25 and 0.12 mg cm⁻². The cell with this composite catalyst showed better performance than the one with the PtRu/C catalyst. When a H₂/100 ppmCO gas was used as the fuel in the single cell test, the cell voltages were measured to be 0.49 and 0.44 V at a current density of 500 mA cm⁻², respectively for the cell with the composite and PtRu/C catalyst.     

Graphene-multi walled carbon nanotube hybrid electrocatalyst support material for direct methanol fuel cell

Nanostructured PtRu and Pt dispersed functionalized graphene-functionalized multi walled carbon nanotubes (PtRu/(f-G-f-MWNT)), (Pt/(f-G-f-MWNT)) nanocomposites have been prepared. Electrochemical studies have been performed for the methanol oxidation using cyclic voltammetry (CV) and chronoamperometry technique. Full cell measurements have been performed using PtRu nanoparticles dispersed on the mixture of functionalized graphene (f-G) and functionalized multi walled carbon nanotubes (f-MWNT) in different ratios as anode electrocatalyst for methanol oxidation and Pt/f-MWNT as cathode catalyst for oxygen reduction reaction in direct methanol fuel cell (DMFC). In addition, full cell measurements have been performed with PtRu/(50 wt% f-MWNT + 50 wt% f-G) and Pt/(50 wt% f-MWNT + 50 wt% f-G) as anode and cathode electrocatalyst respectively. With PtRu/(50 wt% f-MWNT + 50 wt% f-G) as anode electrocatalyst, a high power density of about 40 mW/cm² has been obtained, in accordance with cyclic voltammetry studies. Further enhancement in the power density of about 68 mW/cm² has been observed with PtRu/(50 wt% f-MWNT + 50 wt% f-G) and Pt/(50 wt% f-MWNT + 50 wt% f-G) as electrocatalyst at anode and cathode respectively. These results have been discussed based on the change in the morphology of the f-G sheets due to the addition of f-MWNT.     

Design and synthesis of Pd decorated rGO-MoSe2 2D hybrid network as high performance electrocatalyst toward methanol electrooxidation

Direct methanol fuel cells (DMFCs) have attracted profound interest for development of future green energy sources, which are being powered by methanol as a fuel. The critical problem identified with DMFCs is the deactivation of electrocatalysts resulting from the adsorption of CO during methanol oxidation. In this work, we have employed a new synthetic approach by a green microwave method for the synthesis of hybrid Pd-MoSe₂-rGO and Pd-rGO nanocomposites. The synthesized electrocatalysts were successfully characterized by XRD, which is used to identify the crystalline phases, FESEM and TEM analyses for morphological features, XPS for analyzing the elements constituting the composites surface and Raman spectroscopy for the analysis of molecular structural bonding. Electrocatalytic activity was explored by cyclic voltammetry (CV), chronoamperometry (CA) and CO stripping techniques. Electroactive surface area (EASA) of the developed hybrid electrocatalyst Pd-MoSe₂-rGO (51.81 m² g⁻¹_Pd) was more than 3.4 times superior activity than that of Pd-rGO catalyst (15.30 m² g⁻¹_Pd). It was observed that the synthesized catalyst with 3D cross-linked hybrid network facilitated even distribution of metal nanoparticles and exhibited nearly four times enhanced electrocatalytic activity (1935 mA mg⁻¹_Pd) towards methanol oxidation reaction (MOR) in alkaline medium, compared to Pd-rGO (546 mA mg⁻¹_Pd). Under constant applied potential investigations, catalytic activity of Pd-MoSe₂-rGO was nearly 50 times higher than that of Pd-rGO at the end of about 1 h. The ease of the availability of more active sites and high tolerance against CO poisoning resulted by the insertion of MoSe₂ led to enhanced catalytic activity of Pd-MoSe₂-rGO towards MOR. It is conceived that this synthetic strategy by employing a combination of 2D materials like MoSe₂, graphene and Pd nanoparticles together as building blocks for 3D hybrid network led to efficient electrocatalysts with high surface area and long-term stability towards methanol oxidation. This synthetic strategy exhibits a promising prospect to develop durable and stable electrocatalyst for DMFC applications.     

Ultra-low Pt loading for proton exchange membrane fuel cells by catalyst coating technique with ultrasonic spray coating machine

This paper reports use of an ultrasonic spray for producing ultra-low Pt load membrane electrode assemblies (MEAs) with the catalyst coated membrane (CCM) fabrication technique. Anode Pt loading optimization and rough cathode Pt loading were investigated in the first stage of this research. Accurate cathode Pt coating with catalyst ink using the ultrasonic spray method was investigated in the second stage. It was found that 0.272 mg_Pt/cm² showed the best observed performance for a 33 wt% Nafion CCM when it was ultrasonically spray coated with SGL 24BC, a Sigracet manufactured gas diffusion layer (GDL). Two different loadings (0.232 and 0.155 mg_Pt/cm²) exposed to 600 mA/cm² showed cathode power mass densities of 1.69 and 2.36 W/mg_Pt, respectively. This paper presents impressive cathode mass power density and high fuel cell performance using air as the oxidant and operated at ambient pressure.     

Electrosynthesis of dendritic palladium supported on Ti/TiO2NTs/Ni/CeO2 as high-performing and stable anode electrocatalyst for methanol electrooxidation

Liquid-fueled direct methanol fuel cell (DMFC) is highly promising for low-carbon transportation, but is hindered by high cost and short lifespan of conventional Pt-based electrocatalysts. Herein, we propose a new Pt-free catalyst strategy to exploit high-performing and stable electrocatalyst of DMFC, achieving enhanced electrocatalytic activity and high stability for methanol oxidation reaction (MOR) in alkaline media. A new Pt-free anode catalysts consisting of titanium/reduced-titanium dioxide nanotubes/nickel/cerium dioxide (Ti/r-TiO₂NTs/Ni/CeO₂) nanosupport and uniformly-dispersed Pd dendrites is successfully prepared by a facile three-step electrodeposition route without applying any template or surfactant. Noticeably, the as-prepared Ti/r-TiO₂NTs/Ni/CeO₂–Pd as an anode electrode exhibits superior activity than commercial Pd/C and other electrodes. The obtained large mass activity for Ti/r-TiO₂NTs/Ni/CeO₂–Pd electrode is 1752 mA mg_Pd^?1 for MOR. After successive CV tests of 1000 cycles, Ti/r-TiO₂NTs/Ni/CeO₂–Pd electrode still retained 88.9% of its initial current. The superior performance of Ti/r-TiO₂NTs/Ni/CeO₂–Pd attributes to the large surface area and excellent conductivity, as well as the synergistic effects among nanosupport and Pd dendrites. Therefore, this study will open a new door for high-performance fuel cell applications.     

Synthesis and evaluation of carbon nanotube-supported RuSe catalyst for direct methanol fuel cell cathode

Ruthenium selenide (RuSe) supported on a carbon nanotube (CNT) material, i.e., RuSe/CNT, with a controlled composition (Ru:Se = 1:0.2) was synthesized using a modified polyol method as a model catalyst for direct methanol fuel cell (DMFC) cathode. The prepared electrocatalyst was physically characterized by means of Transmission Electron Microscopy (TEM), X-ray Diffraction (XRD) Spectroscopy and X-ray Photoelectron Spectroscopy (XPS), and its activity for oxygen reduction reaction (ORR) was examined using Linear-Sweep Voltammetry (LSV). In addition, the methanol tolerance was characterized using Electrochemical Impedance Spectroscopy (EIS). It was found that the prepared RuSe/CNT catalyst has good catalyst morphology, uniform and small particle size, and controllable catalyst composition. After subjecting to a proper heat treatment at 400 °C, the electrocatalyst exhibits a good oxygen reduction activity with high methanol tolerance. From both LSV and XPS analyses, it was concluded that a high Se3d_5/2 content plays an important role for oxygen reduction on RuSe/CNT. The EIS characterization also identified the presence of reaction intermediates during the oxygen reduction process. Based on the test results, the mechanisms underlying the dual function of the RuSe/CNT catalyst are proposed. The prepared catalyst was further evaluated for its potential application to DMFC. At 70 °C, the single-cell DMFC integrated with RuSe/CNT exhibited a performance much better than that incorporated with Pt/C counterpart when operated with a high-concentration (i.e., 6 M) methanol fuel. However, substantial improvements are still needed for practical applications.     

PtRu/C-Au/TiO2 electrocatalyst for a direct methanol fuel cell

Au/TiO₂ is added to a PtRu/C electrode to improve the performance of a direct methanol fuel cell (DMFC). A high-throughput-screening test is performed for the fast screening of the loading of Au/TiO₂ on PtRu/C. The electrochemically-active surface area of PtRu/C-Au/TiO₂ and PtRu/C is determined from cyclic voltammetry. In CO-stripping and methanol oxidation voltammetry, PtRu/C-Au/TiO₂ exhibits better activity for CO and methanol oxidation than PtRu/C. The performance of the DMFC is also improved by addition of Au/TiO₂ to the PtRu/C electrode. The CO adsorbed on Pt may move to the surface of the Au/TiO₂ by the interaction between PtRu/C and Au/TiO₂. The improved performance of the PtRu/C-Au/TiO₂ catalyst is explained in terms of preferential oxidation of CO or CO-like poisoning species that are generated during the oxidation of methanol on PtRu/C.     

Application of N-doped carbon nanotube-supported Pt-Ru as electrocatalyst layer in passive direct methanol fuel cell

In this research, nitrogen-doped carbon nanotubes (N-CNT) were prepared through the low-temperature thermal method and used as the support material for the bimetallic catalyst PtRu and Pt nanoparticles. A passive single-cell direct methanol fuel cell (DMFC) was designed and fabricated to investigate and compare the performance of three discrete membrane electrode assemblies (MEA) with carbon black (CB), CNT, and N-CNT as the catalyst support, respectively. Adding N to the structure of CNTs remarkably improves the physical and electrochemical characteristics of the catalyst. More active sites and stronger interaction between support and metal particles lead to the formation of smaller metal clusters and higher surface area as well as superior electrochemical activity. Compared to PtRu/CB and PtRu/CNT, PtRu/N-CNT illustrate 32% and 12% higher surface area, 3 and 1.9 times higher MOR activity, and 62% and 18% higher power output (26.1 mW/cm²), respectively. Moreover, it is revealed that PtRu/N-CNT has long-term stability in the MOR. The research work presented in this paper exhibits the outstanding performance of Pt and PtRu supported on N-CNT in a passive single-cell DMFC.     

Overview of the development of CO-tolerant anode electrocatalysts for proton-exchange membrane fuel cells

Poisoning of Pt anode electrocatalysts by carbon monoxide (CO) is deemed to be one of the most significant barriers to be overcome in the development of proton-exchange membrane fuel cell systems (PEMFCs). The use of CO-tolerant electrocatalysts serves as the most hopeful way to solve this problem. It is well established that Pt-based alloy systems of CO-tolerant electrocatalysts can substantially withstand the presence of CO in the fuel stream. Based on literature starting in 2000, a few efforts have still been conducted at developing a more CO-tolerant anode electrocatalyst than the traditional Pt/C or PtRu/C systems. This review introduces and discusses these efforts.Pt-based electrocatalysts, including PtSn/C, PtMo/C (atomic ratio = 5:1), PtRuMo/C (Mo = 10 wt.%), PtRu–H_xMoO₃/C and PtRu/(C nanotubes), appear to be poisoned by CO at the same, or a lower, level than traditional Pt/C or PtRu/C electrocatalysts. Platinum-free electrocatalysts, such as PdAu/C, have proven to be less strongly poisoned by CO than PtRu/C counterparts at temperatures of 60 °C.A greater tolerance to CO can be achieved by modifying the structure of the electrocatalyst. This involves the use of a composite or double-layer that is designed to make the CO react with one of the electrocatalyst in advance while the main hydrogen reacts at another layer with a traditional Pt/C electrocatalyst.     

Synthesis of ultrafine low loading Pd–Cu alloy catalysts supported on graphene with excellent electrocatalytic performance for formic acid oxidation

Here, surfactant free composite catalysts (Pd–Cu/rGO) with Pd–Cu alloy nanoparticles uniformly distributed on graphene sheets are successfully prepared via a facile hydrothermal approach. Compared with pure Pd/rGO catalyst, the introduction of copper could dramatically enhance the performance of the catalyst in the electrocatalytic formic acid oxidation (FAO) due to the strain effect and the ligand effect. With the optimized atomic ratio of 3:1 between palladium and copper, the alloy nanoparticle shows the smallest size of 2.12 nm, thus endowing the composite catalyst with highest catalytic efficiency. With Pd load as low as 14.5%, a maximum mass current density of 1580 mA mg_Pd⁻¹, and residual current of 69.93 mA mg_Pd⁻¹ at 3000 s was achieved with our Pd₃Cu₁/rGO catalyst in the electrocatalytic FAO process.