Data from experiments with both rotating disc electrodes (RDEs) and gas diffusion electrodes (GDEs) are used to investigate the properties of the spinels, Co3O4 and NiCo2O4, as bifunctional oxygen electrocatalysts. Emphasis is placed on catalyst compositions and electrode structures free of carbon. Oxygen evolution and reduction occur at surfaces where the transition metals are in different oxidation states but the surface can be repeatedly cycled between these two states without significant change. It is shown that carbon-free, NiCo2O4 catalysed GDEs can be fabricated using structures based on stainless steel cloth or nickel foam. Those based on nickel foam can be cycled extensively and allow both O2 evolution and reduction at current densities up to 100 mA cm−2.

•Fabrication and development of a carbon free bifunctional gas diffusion electrode.•Good stability and overpotentials on cycling at 50 mA cm−2 for >50 cycles.•Operational up to current densities of 100 mA cm−2.The fabrication of a gas diffusion electrode (GDE) without carbon components is described. It is therefore suitable for use as a bifunctional oxygen electrode in alkaline secondary batteries. The electrode is fabricated in two stages (a) the formation of a PTFE-bonded nickel powder layer on a nickel foam substrate and (b) the deposition of a NiCo2O4 spinel electrocatalyst layer by dip coating in a nitrate solution and thermal decomposition. The influence of modifications to the procedure on the performance of the GDEs in 8 M NaOH at 333 K is described. The GDEs can support current densities up to 100 mA cm−2 with state-of-the-art overpotentials for both oxygen evolution and oxygen reduction. Stable performance during >50 successive, 1 h oxygen reduction/evolution cycles at a current density of 50 mA cm−2 has been achieved.

We report borrowed surface-enhanced Raman scattering (SERS) at Pd and Pt films deposited on Au sphere segment void (SSV) SERS substrates and show that ultrathin, pinhole-free Pd and Pt films could be easily achieved by choosing constant-current deposition for the Pd deposition and under-potential deposited Cu-mediated deposition for the Pt deposition. The surface enhancement achieved from the Pd and Pt films was reproducible, owing to the ordered SSV structure of their surfaces, and borrowed additional enhancement from the long-range electromagnetic (EM) fields generated by the underlying Au SSV substrate. SERS experiments and theoretical simulations indicate that the distance over which the EM fields generated by a concave Au SSV surface can be transferred to the surface of the transition-metal films is approximately an order of magnitude larger than that for a convex sphere surface. This longer range of the EM fields allowed deposition of thicker, more robust Pd and Pt films while retaining the borrowed enhancement. These properties make such Pd and Pt films attractive as SERS surfaces to reveal surface species and reactive intermediates on these two typical electrocatalyst materials.

Carbon supported Au@Pd core@shell nanoparticles were prepared using two methods based on displacement of a Cu-under potential deposited (upd) layer; the standard method, in which a single Cu-upd layer is formed and then displaced, and a Cu-upd-mediated deposition method, wherein the Pd displaces the Cu-upd layer during the Cu deposition. The resulting materials were characterized using in situ extended X-ray absorption fine structure as a function of the applied potential in an electrochemical cell at both the Au L3 and Pd K absorption edges. This detailed structural analysis shows that the standard, single Cu-upd layer method results in the formation of Pd clusters or islands on the Au core rather than a complete monolayer shell, while the Cu-upd-mediated method produces a mixed/alloyed PdAu shell.

The underpotential deposition (upd) of a Cu shell on a non-Pt nanoparticle core followed by galvanic displacement of the Cu template shell to form core–shell electrocatalyst materials is one means by which the Pt-based mass activity targets required for commercialization of PEM fuel cells may be reached. In situ EXAFS measurements were conducted at both the Au L3 and the Cu K absorption edges during deposition of Cu onto a carbon-supported Au electrocatalyst to study the initial stages of formation of such a core–shell electrocatalyst. The Au L3 EXAFS data obtained in 0.5 mol dm–3 H2SO4 show that the shape of the Au core is potential dependent, from a flattened to a round spherical shape as the Cu upd potential is approached. Following the addition of 2 mmol dm–3 Cu, the structure was also measured as a function of the applied potential. At +0.2 V vs Hg/Hg2SO4, the Cu2+ species was found to be a hydrated octahedron. As the potential was made more negative, single-crystal studies predict an ordered bilayer of sulfate anions and partially discharged Cu ions, followed by a complete/uniform layer of Cu atoms. In contrast, the model obtained by fitting the Au L3 and Cu K EXAFS data corresponds first to partially discharged Cu ions deposited at the defect sites in the outer shell of the Au nanoparticles at −0.42 V, followed by the growth of clusters of Cu atoms at −0.51 V. The absence of a uniform/complete Cu shell, even at the most negative potentials investigated, has implications for the structure, and the activity and/or stability, of the core–shell catalyst that would be subsequently formed following galvanic displacement of the Cu shell.

We demonstrate that by combining silver nanoparticles and structured gold SSV surfaces the SERS for those molecules that bridge the nanoparticle–cavity gap is preferentially enhanced using 4-mercaptoaniline and 4-mercaptobenzoic acid as examples.

The Ru–CO bond of CO adsorbed on a Ru modified Pt/C fuel cell catalyst has been directly probed by in situ EXAFS at the Ru K-edge, providing evidence of a CO:metal surface atom ratio greater than 1:1 and that CO is adsorbed at bridging sites associated with Ru atoms at the surface of the catalyst nanoparticles. This result illustrates the limitations of single crystal models as representations of the bonding of adsorbed species at nanoparticle surfaces.

Ultraviolet laser excited surface-enhanced Raman scattering was obtained for the first time at the well ordered palladium sphere segment void (SSV) nanostructures, using adenine as the probe molecule, and the UV-SERS enhancement is found to be correlated well with the plasmon absorption of Pd SSVs in the UV region.

A controlled surface reaction technique has been successfully employed to prepare a series of Pt modified Pd/C (Pt/Pd/C) and Pd modified Pt/C (Pd/Pt/C) catalysts. The resulting catalyst materials were characterised by TEM, XRD, electrochemistry, and EXAFS techniques. In the case of the Pd/Pt/C carbon catalysts, core–shell structural arrangements were found, with a 0.04 Å contraction of the Pd–Pd bond distance for the 1 Pd/Pt/C being observed. A greater degree of alloying was found for the Pt/Pd/C catalysts where the surface had a mixed composition with a large proportion of the Pt in the interior of the nanoparticle. However, strong Pt characteristics were exhibited in the voltammetry of Pt/Pd/C catalysts, most notably a large increase in the stability with respect to the electrochemical environment compared to Pd alone.

A series of carbon supported PtRu bimetallic catalysts with varying Pt:Ru ratio were prepared and characterised using ex situ and in situXRD, in situ EXAFS at 0 V vs.RHE, ex situ XPS and monolayer CO stripping voltammetry. Although the catalysts were found to be well mixed/alloyed, with no evidence of unalloyed Ru (oxides) present, the surfaces of the electrocatalyst nanoparticles were found to be enriched with Pt compared to the nominal bulk composition. The methanol oxidation activities of the catalysts were determined in 1.0 mol dm−3 H2SO4. In agreement with published studies of polycrystalline bulk PtRu alloys the catalyst with a 0.6 surface fraction of Pt was found to give the best methanol oxidation activity at 30 °C. However, at 80 °C a greater surface fraction of Ru could be tolerated, with some activity at low current densities found for a Pt surface fraction as low as 0.2. The results support the conclusion that a limited amount of methanol dehydrogenation occurs at Ru sites or Ru dominated surface ensembles at 80 °C.

The CO2 tolerance exhibited by PtRu/C is known to be greater than that of PtMo/C catalysts in contrast to the trend in CO tolerance. In this manuscript the origins of these differences are investigated in a cyclic voltammetric investigation of the potential dependence of the poisoning of Pt/C, PtRu/C and PtMo/C anode catalyst electrodes in a miniature PEM fuel cell when exposed to pure CO, pure CO2, or 25% CO2 in H2. The results show that the difference in the mechanisms of improved CO tolerance, compared to a Pt/C reference catalyst, of PtRu and PtMo explain the decreased CO2 tolerance of PtMo compared to PtRu; at PtRu the mechanism is intrinsic (water activation at Ru sites), whilst at PtMo the mechanism relies on the turn-over the Mo(IV/VI) redox couple.

Ruthenium modified carbon supported platinum catalysts have been shown to have a similar activity towards carbon monoxide oxidation as conventionally prepared bimetallic PtRu alloy catalysts. In this study the effect of the applied electrode potential and potential cycles on the location and oxidation state of the Ru species in such Ru modified Pt/C catalysts was investigated using in situ EXAFS collected at both the Ru K and Pt L3 absorption edges. The as prepared catalyst was found to consist of a Pt core with a Ru oxy/hydroxide shell. The potential dependent data indicated alloying to form a PtRu phase at 0.05 V versus RHE and subsequent dealloying to return to the Ru oxy/hydroxide decorated Pt surface at potentials greater than 0.7 V. The Ru–O distances obtained indicate that both Ru3+ and Ru4+ species are present on the surface of the Pt particles at oxidising potentials; the former is characteristic of the as prepared Ru modified Pt/C catalyst and following extensive periods at potentials above 0.7 V and the latter of the Ru oxide species on the PtRu alloy.

Templated electrodeposition of gold to produce thin (<1 μm) films containing a close packed hexagonal array of uniform sphere segment voids is shown to give surfaces which show strong surface enhancement for Raman scattering from molecules adsorbed at the surface. The magnitude of this is enhancement is determined by the precise geometry of the surface and depends on the choice of void diameter and film thickness. The resulting SER active surfaces are stable, reusable, give reproducible surface enhancement and can be used for in situ electrochemical SERS studies.

A miniature proton exchange membrane (PEM) fuel cell has been designed to enable in situ XAS investigations of the anode catalyst using fluorescence detection. The development of the cell is described, in particular the modifications required for elevated temperature operation and humidification of the feed gasses. The impact of the operating conditions is observed as an increase in the catalyst utilisation, which is evident in the EXAFS collected at the Pt LIII and Ru K edges for a PtRu/C catalyst. The Pt component of the catalyst was found to be readily reduced by hydrogen in the fuel, while the Ru was only fully reduced under conditions of good gas flow and electrochemical contact. Under such conditions no evidence of O neighbours were found at the Ru edge. The results are interpreted in relation to the lack of surface sensitivity of the EXAFS method and indicate that the equilibrium coverage of O species on the Ru surface sites is too low to be observed using EXAFS.

In situ EXAFS (extended X-ray absorption fine structure), in situ XRD (X-ray diffraction) and electrochemical studies have been used to investigate the palladium hydride phases of carbon supported palladium nanoparticles as a function of applied potential. Electrochemical investigations showed an increase in the hydrogen to palladium ratio with an increasingly negative potential. The H/Pd ratio could be divided into four distinct regions, which described the palladium hydride phase present; the α-phase, a mixture of the α- and β-phases, the β-phase, and a hyperstoichiometric region. The β-hydride phase stoichiometry obtained from the electrochemical data corresponded to PdH. However, the composition obtained from the lattice expansions observed from the in situ EXAFS and XRD, 3.3% and 3.8%, correspond to compositions of PdH0.59 to PdH0.68. The excess hydrogen and hyperstoichiometric amounts found at more negative potentials are attributed to either spillover on to the carbon support or trapping and subsequent reoxidation of H2 in the porous electrode structure.

We present a study of the coverage and temperature dependence of the Pt–CO stretching vibration of CO adsorbed on both the reconstructed Pt{1 1 0}-(1×2) and the unreconstructed Pt{1 1 0}-(1×1) surfaces. The metal–carbon stretching vibration is shown to be a sensitive probe of the structure of the underlying Pt{1 1 0} surface. As a function of coverage, the position of the adsorption peak shifts from 471 to 480 cm−1 at 310 K, accompanying the adsorbate induced lifting of the reconstruction. At 115 K, where the reconstruction is not lifted, the absorption band remains centered at 466 cm−1, however the FWHM increases from 6 cm−1 at 0.05 L to 15 cm−1 at saturation. The band at 466 cm−1 is attributed to initial adsorption into atop sites on the atomic ridges followed by adsorption into atop sites on the (1 1 1) microfacets. The sensitivity of the synchrotron far-infrared RAIRS technique has allowed the lifting of the reconstruction to be followed as a function of temperature and, for the first time, allowed detection of localised lifting of the (1×2) reconstruction at a temperature 50 K lower than previously reported.

The utility of in situ X-ray absorption spectroscopy (XAS) in determining structural parameters, through analysis of the extended X-ray absorption fine structure (EXAFS), and electronic perturbations, through a white line analysis of the X-ray absorption near edge structure (XANES), is demonstrated for Pt/C, PtRu/C and PtMo/C fuel cell electrodes. The results provide verification that the enhancement of CO tolerance of the alloy catalysts occurs via an intrinsic mechanism for the PtRu alloy, whilst a promotion mechanism is in operation for the PtMo alloy. Preliminary results of an in situ powder X-ray diffraction (XRD) method which utilises synchrotron radiation (SR) and a curved image plate detector are also presented, using Pd/C as an example. The lattice expansion upon formation of the β-hydride is clearly observed.

We demonstrate that by combining silver nanoparticles and structured gold SSV surfaces the SERS for those molecules that bridge the nanoparticle–cavity gap is preferentially enhanced using 4-mercaptoaniline and 4-mercaptobenzoic acid as examples.

A series of carbon supported PtRu bimetallic catalysts with varying Pt:Ru ratio were prepared and characterised using ex situ and in situXRD, in situ EXAFS at 0 V vs.RHE, ex situ XPS and monolayer CO stripping voltammetry. Although the catalysts were found to be well mixed/alloyed, with no evidence of unalloyed Ru (oxides) present, the surfaces of the electrocatalyst nanoparticles were found to be enriched with Pt compared to the nominal bulk composition. The methanol oxidation activities of the catalysts were determined in 1.0 mol dm−3 H2SO4. In agreement with published studies of polycrystalline bulk PtRu alloys the catalyst with a 0.6 surface fraction of Pt was found to give the best methanol oxidation activity at 30 °C. However, at 80 °C a greater surface fraction of Ru could be tolerated, with some activity at low current densities found for a Pt surface fraction as low as 0.2. The results support the conclusion that a limited amount of methanol dehydrogenation occurs at Ru sites or Ru dominated surface ensembles at 80 °C.

A controlled surface reaction technique has been successfully employed to prepare a series of Pt modified Pd/C (Pt/Pd/C) and Pd modified Pt/C (Pd/Pt/C) catalysts. The resulting catalyst materials were characterised by TEM, XRD, electrochemistry, and EXAFS techniques. In the case of the Pd/Pt/C carbon catalysts, core–shell structural arrangements were found, with a 0.04 Å contraction of the Pd–Pd bond distance for the 1 Pd/Pt/C being observed. A greater degree of alloying was found for the Pt/Pd/C catalysts where the surface had a mixed composition with a large proportion of the Pt in the interior of the nanoparticle. However, strong Pt characteristics were exhibited in the voltammetry of Pt/Pd/C catalysts, most notably a large increase in the stability with respect to the electrochemical environment compared to Pd alone.

Ultraviolet laser excited surface-enhanced Raman scattering was obtained for the first time at the well ordered palladium sphere segment void (SSV) nanostructures, using adenine as the probe molecule, and the UV-SERS enhancement is found to be correlated well with the plasmon absorption of Pd SSVs in the UV region.