Composition-tunable PtCu porous nanowires as highly active and durable catalyst for oxygen reduction reaction

To accelerate the commercialization of fuel cells, many efforts have been made to develope highly active and durable Pt-based catalyst for oxygen reduction reaction (ORR). Herein, PtCu porous nanowires (PNWs) with controllable composition are synthesized through an ultrasound-assisted galvanic replacement reaction. The porous structure, surface strain, and electronic property of PtCu PNWs are optimized by tuning composition, which can improve activity for ORR. Electrochemical tests reveal that the mass activity of Pt_0.5Cu_0.5 PNWs (Pt/Cu atomic ratio of 1:1) reaches 0.80 A mg_Pt^?1, which is about 5 times higher than that of the commercial Pt/C catalyst. Notably, the improved activity of the porous nanowire catalyst is also confirmed in the single-cell test. In addition, the large contact area with the carrier and internal interconnection structure of Pt_0.5Cu_0.5 PNWs enables them to exhibit much better durability than the commercial Pt/C catalyst and Pt_0.5Cu_0.5 nanotubes in accelerated durability test.     

Boosting the activity of FeOOH via integration of ZIF-12 and graphene to efficiently catalyze the oxygen evolution reaction

Transition metal oxyhydroxides have been used as promising electrocatalysts for water splitting however, their catalytic activity is restricted due to low surface area and poor conductivity. Herein, we report novel composite FeOOH@ZIF-12/graphene composite as electrocatalyst for water oxidation, whereby ZIF-12 provide extra surface for the FeOOH dispersion whilst graphene act as excellent electron mediator. The composite shows a low overpotential value of 291 mV to attain a current density of 10 mA cm^?2 and a low Tafel slope value of 78 mV dec^?1. The catalyst offers a maximum current density of 101 mA cm^?2, while it gives a turnover frequency (TOF) value of 0.031 s^?1 at an overpotential of 291 mV only. The excellent activity and remarkable stability of composite is attributed to highly conductive and porous support.     

Investigation of thermal and electrochemical degradation of fuel cell catalysts

A significant problem hindering large-scale implementation of proton exchange membrane (PEM) fuel cell technology is the loss of performance during extended operation and automotive cycling. Recent investigations of the deterioration of cell performance have revealed that a considerable part of the performance loss is due to the degradation of the electrocatalyst. In this study, an attempt is made to experimentally simulate the degradation processes such as carbon corrosion and platinum (Pt) surface area loss using an accelerated thermal sintering protocol. Two types of Tanaka fuel cell catalyst samples were heat-treated at 250 °C in humidified helium (He) gas streams and several oxygen (O₂) concentrations. The catalysts were then cycled electrochemically in pellet electrodes to determine the hydrogen adsorption (HAD) area and its evolution in subsequent electrochemical cycling. Samples that had undergone different degrees of carbon corrosion and Pt sintering were characterized for changes in carbon mass, active Pt surface area, BET (Brunauer, Emmett and Teller) surface area, and Pt crystallite size. Studies of the effect of oxygen and water concentration on two Tanaka catalysts, dispersed on carbon supports with varying BET areas, revealed that carbon oxidation in the presence of Pt follows two pathways: an oxygen pathway that leads to mass loss due to formation of gaseous products, and a water pathway that results in mass gains, especially for high BET area supports. These processes may be assisted by the formation of highly reactive OH and OOH type radicals. Platinum surface area loss, measured at varying oxygen concentrations and as a function of sintering time using X-ray diffraction (XRD), CO chemisorption, and electrochemical hydrogen adsorption, reveal an important role for carbon corrosion rather than an increase in Pt particle size for the surface area loss. Platinum surface area loss during 10 h of thermal degradation was equivalent to electrochemical degradation observed over 500 cycles for a Tanaka Pt/Vulcan electrode cycled between 0 and 1.2 V (normal hydrogen electrode-NHE). Carbon mass loss observed for 5 h of thermal degradation was comparable to that obtained during a potential hold for 86 h at 1.2 V (NHE) and 95 °C for the same catalysts.     

Synthesis and electrocatalytic performance of MWCNT-supported Ag@Pt core–shell nanoparticles for ORR

Ag@Pt core–shell nanoparticles with different Ag/Pt ratios were supported on multi walled carbon nanotubes (MWCNTs) and used as electrocatalysts for PEMFC. The morphology of the electrocatalyst samples was characterized by XRD and HRTEM. It was found that the Ag@Pt/MWCNTs catalyst exhibited a core–shell nanostructure. And the CV and LSV results demonstrated that such core–shell materials exhibited attractive electrocatalytic activity. Moreover, the specific electrochemically active area (EAS) of the Ag@Pt/MWCNTs catalyst is 70.63 m² g⁻¹, which is higher than the values reported in the literature.     

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.     

Investigation of carbon-supported Au hollow nanospheres as electrocatalyst for electrooxidation of sodium borohydride

A carbon-supported Au hollow nanospheres composite electrocatalyst was prepared in aqueous solution with Co nanoparticles as sacrificial templates at room temperature. The electrocatalyst was characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), energy dispersion X-ray (EDX) spectra and electrochemical tests. The results showed that carbon-supported Au hollow nanospheres were porous, and composed of discrete Au nanoparticles with the crystallite size of about 6 nm. For comparison, the electrocatalytic performances of both carbon-supported Au hollow nanospheres and carbon-supported Au solid nanoparticles on borohydride electrooxidation in fuel cells were investigated by cyclic voltammetry, chronoamperometry, and chronopotentiometry. The fundamental electrochemical test results indicated that the electrocatalytic activity of carbon-supported Au hollow nanospheres is much better than that of carbon-supported Au solid nanoparticles.     

Methanol electro-oxidation by a ternary Pt–Ru–Cu catalyst identified by a combinatorial approach

Composition optimization of the ternary Pt–Ru–Cu system for the methanol electro-oxidation reaction (MOR) was performed by combinatorial synthesis and high-throughput screening methods. A thin film library of the Pt–Ru–Cu system was prepared by a sputtering system to generate 63 different compositions. The compositions were characterized in parallel by a multichannel multielectrode analyzer. The highest MOR activity was observed for the Pt₆₆Ru₁₇Cu₁₇ composition. The Pt₆₆Ru₁₇Cu₁₇/C composition was synthesized and characterized as a powder catalyst to verify the performance of this new composition. During cyclic voltammetry tests, the Pt₆₆Ru₁₇Cu₁₇/C catalyst showed less dissolution and irreversible oxidation of Ru than a Pt₅₀Ru₅₀/C catalyst, with increasing number of cycles. In MOR activity measurement experiments, the Pt₆₆Ru₁₇Cu₁₇/C catalyst exhibited 26 and 86% higher activities in cyclic and chronoamperometric tests, respectively, than those of the Pt₅₀Ru₅₀/C catalyst.     

One-step fabrication of heterostructured CoNi-LDH@NiCo alloy for effective alkaline hydrogen evolution

Construction of heterostructured electrocatalyst with interface effect is an effective strategy for enhancing the alkaline hydrogen evolution efficiency, whereas this process often requires complex treatments. Herein, we proposed a one-step electrodeposition method to obtain heterostructured CoNi-LDH@NiCo alloy on Ni foam (NF) through a competition reduction between NO₃^? group and metal cations in the electrolyte. The HER performance for the CoNi-LDH@NiCo alloy achieved the current density of 10 mA cm^?2 at overpotential of 69 mV in 1 M KOH solution, improved 60% for η₁₀ by comparing with the pristine NiCo alloy. Utilizing the specialized adsorption of CoNi-LDH for H₂O and the featured attractiveness of NiCo alloy for H atom, the interface effect of the heterostructure electrocatalyst accelerated the dissociation of water molecules and elevated the catalytic kinetics dramatically. This work points out a potential approach towards the easy construction of inexpensive heterostructured electrocatalysts for HER activity in alkaline medium.     

High-performance core–shell PdPt@Pt/C catalysts via decorating PdPt alloy cores with Pt

A core–shell structured low-Pt catalyst, PdPt@Pt/C, with high performance towards both methanol anodic oxidation and oxygen cathodic reduction, as well as in a single hydrogen/air fuel cell, is prepared by a novel two-step colloidal approach. For the anodic oxidation of methanol, the catalyst shows three times higher activity than commercial Tanaka 50 wt% Pt/C catalyst; furthermore, the ratio of forward current I_f to backward current I_b is high up to 1.04, whereas for general platinum catalysts the ratio is only ca. 0.70, indicating that this PdPt@Pt/C catalyst has high activity towards methanol anodic oxidation and good tolerance to the intermediates of methanol oxidation. The catalyst is characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The core–shell structure of the catalyst is revealed by XRD and TEM, and is also supported by underpotential deposition of hydrogen (UPDH). The high performance of the PdPt@Pt/C catalyst may make it a promising and competitive low-Pt catalyst for hydrogen fueled polymer electrolyte membrane fuel cell (PEMFC) or direct methanol fuel cell (DMFC) applications.