Role of perfluorosulfonic ionomer as protective agent against strong adsorption of (bi)sulfate anions. Relevance in the determination of the area of Pt/C electrocatalysts

This work aims to shed light on the wide dispersion of the values of the area of Pt/C electrodes reported when evaluated by means of the thin-film electrode approach. The effect of the Perfluorosulfonic Ionomer (PFSI) content of the electrodes and the nature of the electrolyte are discussed. The results disclose that the area of the Pt electrodes evaluated by electrochemical techniques is related to the actual PFSI content on the electrode and to the nature of the electrolyte. Using HClO₄ as electrolyte, electrode area values are independent of the PFSI content. On the contrary, if experiments are recorded in H₂SO₄, the electrode area value increases with the increasing PFSI content, irrespectively of the Pt loading. Such effect is ascribed to the interaction of the sulfonic groups from the PFSI with the surface of the Pt nanoparticles, avoiding the strong adsorption of the bisulfate anions.     

In situ spectroelectrochemical measurements during the electro-oxidation of ethanol on WC-supported Pt-black. Part II: Monitoring of catalyst aging by in situ Fourier transform infrared spectroscopy

As a continuation of a project on the spectroelectrochemical analysis of long-term behaviour of WC-supported Pt electrocatalysts (for SFG results, see part I: [1]), in this paper we report in situ FT-IR spectroscopy experiments, carried out during prolonged electro-oxidation of ethanol on Pt-black. From the analytical point of view, as expected, FT-IR spectra showed the presence of adsorbed acetic acid and ethanol, in addition to the well-known, dominant species: linearly adsorbed CO (2044-2063 cm⁻¹) and solution-phase CO₂ (2345 cm⁻¹). As far as quantitative spectroscopic results are concerned, a notable sensitivity of the interfacial chemistry to catalyst aging could be highlighted by this approach. The spectra recorded in three subsequent series of potential-cycling experiments showed a clear-cut dependence of spectral patterns and peak intensities, on the applied potential and on the oxidation duration. Qualitative spectral changes seem to suggest - coherently with in situ SFG results obtained with the same system [1] - that electrocatalyst aging correlates with a higher surface coverage with ethanol as compared with acetic acid. Quantitative analysis, based on fitting with Lorentzian lineshapes, yields information that can be used as a molecular-level diagnostic of the modification of the catalyst-adsorbate structure.     

Enhanced activity and stability of Pt/C fuel cell anodes by the modification with ruthenium-oxide nanosheets

Ruthenium-oxide nanosheet (RuO₂ns) crystallites with thickness less than 1 nm were prepared via chemical exfoliation of a layered potassium ruthenate and deposited onto carbon supported platinum (Pt/C) as a potential co-catalyst for fuel cell anode catalysts. The electrocatalytic activity towards carbon monoxide and methanol oxidation was studied at various temperatures for different RuO₂ns loadings. An increase in electrocatalytic activity was evidenced at temperatures above 40 °C, while little enhancement in activity was observed at room temperature. The RuO₂ns modified Pt/C catalyst with composition of RuO₂:Pt = 0.5:1 (molar ratio) exhibited the highest methanol oxidation activity. CO-stripping voltammetry revealed that RuO₂ns promotes oxidation of adsorbed CO on Pt. In addition to the enhanced initial activity, the RuO₂ns modified Pt/C catalyst exhibited improved stability compared to pristine Pt/C against consecutive potential cycling tests.     

Phytic acid-coated titanium as electrocatalyst of hydrogen evolution reaction in alkaline electrolyte

The phytic acid-coated titanium (IP6/Ti) electrode was prepared through a simple drop-drying process, with an aim of improving electrocatalytic activity toward the hydrogen evolution reaction (HER). Scanning electron microscope and X-ray photoelectron spectroscopy showed that the IP6 coated the substrate surface uniformly and completely. Evaluation of the electrode activity was carried out in 1.0 M NaOH by linear polarization, electrochemical impedance spectroscopy (EIS) and chronopotentiometry. The kinetic parameters obtained from Tafel curves reveal that the IP6 coating can enhance the exchange current density of the HER by 489 times compared to the bare Ti, and reduce the HER activation energy by nearly 50%. The EIS data prove that the charge transfer resistance of the HER was considerably reduced due to the IP6 coating, with a decrease in real surface area of the electrode. The catalytic effect of IP6 is due to an improvement in the charge transfer kinetics of the HER. This work indicates that IP6 may be a potent candidate as a catalyst for hydrogen energy production.     

Facile one-pot synthesis of binder-free nano/micro structured dendritic cobalt activated nickel sulfide: a highly efficient electrocatalyst for oxygen evolution reaction

Reasonable design and preparation of non-noble metal electrocatalysts with predominant catalytic activity and long-term stability for oxygen evolution reaction (OER) are essential for electrocatalytic water splitting. Ni foam (NF) is highlighted for its 3D porous structure, impressive conductivity and large specific surface area. Herein, nano/micro structured dendritic cobalt activated nickel sulfide grown on 3D porous NF (Co–Ni₃S₂/NF) has been successfully synthesized by one-step hydrothermal method. Due to the ingenious incorporation of Co, Co–Ni₃S₂/NF electrode shows auspicious electrocatalytic performance for OER compared with Ni₃S₂/NF electrode. As a result, Co–Ni₃S₂/NF needs overpotential of only 274 and 459 mV at current density of 10 and 50 mA cm⁻², respectively, while Ni₃S₂/NF requires overpotential of 344 and 511 mV. At potential of 2.0 V (vs. RHE), Co–Ni₃S₂/NF displays current density of 191 mA cm⁻², while Ni₃S₂/NF just attains current density of only 135 mA cm⁻². Moreover, Co–Ni₃S₂/NF demonstrates excellent stability for uninterrupted OER in alkaline electrolyte. The strategy of designing and preparing cobalt activated nickel sulfide grown on NF renders a magnificent prospect for the development of metal-sulfide-based oxygen evolution catalysts with excellent electrocatalytic performances.     

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.     

Study of a proton exchange membrane fuel cells catalyst subjected to anodic operating conditions, by synchrotron-based scanning photoelectron microscopy (SPEM) and high lateral-resolution X-ray photoelectron spectroscopy

In this paper we report an investigation of the degradation of the Pt/C electrocatalyst of an anodic membrane-electrode assembly (MEA) after 1000 h of operation in a laboratory single-cell PEMFC, using synchrotron-based space-resolved photoelectron spectroscopy. This study is complemented by the analysis of a pristine MEA and reference materials, as well as by electrochemical measurements, SEM imaging and energy-dispersive X-ray fluorescence spectroscopy (EDX). Catalyst ageing correlates with a corrugation of morphology, as observed by SEM and scanning photoelectron microscopy (SPEM), corresponding to Pt nanoparticle agglomeration. Moreover - on the basis of high lateral resolution SPEM, X-ray photoelectron spectroscopy (XPS) and EDX analyses, - we found that, after operation, Pt is transported onto the fibres of the gas-diffusion layer (GDL). Space-resolved XPS shows a peak shift of the Pt 4f_7/2 level to higher and lower binding energies with respect to Pt(1 1 1) and pristine Pt black, respectively, corresponding to nanocrystallinity in the first case and agglomeration in the second one. No oxidised Pt was found in any location of the anodically used MEA.     

Tungsten carbide nanofibers prepared by electrospinning with high electrocatalytic activity for oxygen reduction

Tungsten carbide (WC) nanofibers with ultrafine diameters were synthesized by carbonizing the as-spun ammonium metatungstate (AMT) and polyvinyl pyrrolidone (PVP) composite fiber precursors. The morphologies of the WC nanofiber products were closely related to the electrospinning concentrations of AMT and PVP. Raman spectra and high resolution TEM (HR-TEM) testified that the surface of the WC nanofibers was coated by a carbon layer with a thickness of several nanometers, which could be removed to a great degree by NH₃ etching at high temperature. Cyclic voltammetry (CV) and rotating disk electrode (RDE) test results showed that the carbon-coated WC nanofibers had good electrocatalytic activities and stabilities during oxygen reduction reaction (ORR), both of which could be further improved by NH₃ post-treatment at high temperature. The catalytic roles of the WC nanofiber samples for ORR probably originated from the WC sites, but not excluding some contributions of the surface carbon species.     

Development of bifunctional Mo doped ZnAl2O4 spinel nanorods array directly grown on carbon fiber for supercapacitor and OER application

Electrochemical energy storage and water splitting strategies may be greatly improved with proper structural design and doping techniques. In the present study, molybdenum-doped ZnAl₂O₄ loaded on carbon fiber (Mo–ZnAl₂O₄/CF) was fabricated via a simple hydrothermal synthetic approach. Due to its unique hierarchical nanostructures and enhanced electrical, structural topologies, Mo-doped ZnAl₂O₄ demonstrates exceptional supercapacitor performance and electrocatalytic oxygen evolution reaction activity. The Mo-doped ZnAl₂O₄ electrode material exhibited 1477.63 F g^?1 specific capacitance, 46.57 Wh Kg^?1 specific energy and specific power of 476.4 W kg^?1 at 1 A g^?1. After 5000 cycles, the pseudo supercapacitor retains 97.46% of its capacitance and displays stable behavior over 50 h. During the OER reaction, the Mo–ZnAl₂O₄/CF as an electrocatalyst rapidly self-reconstructs, resulting in many oxygen vacancies, and causes a lower 38 mV dec^?1 Tafel slope and overpotential potential of 255 mV to achieved 10 mA cm^?2 current flow and responsible for the excellent stability of the electrocatalyst. These findings suggest that multifunctional materials based electrode for electrical energy conversion and storage become more efficient and stable by using Mo for doping to generate porous hierarchical structures and local amorphous phases.     

Nanoengineering of ZnCo2O4@CoMoO4 heterogeneous structures for supercapacitor and water splitting applications

A hybrid ZnCo₂O₄@CoMoO₄ heterogeneous structure deposited onto nickel foam was synthesized via a two-step hydrothermal process. The results demonstrate that the hybrid architecture exhibits excellent electrochemical performance, including the specific capacitance of 1040C g^?1 at 1 A g^?1 for hybrid structures, high energy density of 87.3 Wh kg^?1 at a power density of 2700 W kg^?1 for an as-assembled supercapacitor and excellent cycle stability with a capacity retention of 99% undergoing 8000 charge-discharge for the device. Moreover, it also shows favorable electrocatalytic activity with low overpotentials of 237 mV at 20 mA cm^?2 for oxygen evolution reaction and 114 mV at 10 mA cm^?2 for hydrogen evolution reaction, and low cell voltage of 1.54 V at 10 mA cm^?2 for overall water splitting. In addition, the stability maintains well for the long-term use of 13 h. We believe that this hybrid ZnCo₂O₄@CoMoO₄ heterogeneous structure could be a promising candidate for future energy storage and conversion.