Large areal capacitance electrodes made of ruthenium oxide on highly porous gold current collectors are realized by an attractive approach. The hybrid structure exhibits a capacitance in excess of 3 F cm(-2) and an areal energy density for all-solid-state microsupercapacitors that is comparable to those of microbatteries.

Stable PtAu alloy colloids with a wide range of compositions were prepared using pulsed laser ablation on single metal-mixture targets in water. The concentration of Pt in the alloys can be tuned by varying the Pt/Au ratio in the targets, which are made by compression molding a mixture of Pt and Au powders at different ratios. Such fabricated PtAu alloy nanoparticles (NPs) show a face-centered cubic structure, and their composition basically follows that of their corresponding targets. The effect of aqueous solution pH and ablating laser fluence on the formation and structure of alloy NPs was further investigated. It is found that PtAu alloy colloids of identical composition can be achieved over a pH range extending from 4.0 to 11.0 and at fluences varying from 4 to 150 J cm–2 as long as the targets of the same composition are used. This finding suggests that alloy formation is essentially insensitive to both factors in certain ranges, and the method developed herein for the alloy NP formation is quite robust. Moreover, the surface composition, estimated from electrochemical measurements, is identical to the overall composition of the NPs estimated from Vegard’s law and X-ray diffraction data, which is a strong indication of the uniform composition on the surface and in the interior of these alloy NPs.

Crossed-beam pulsed laser deposition in a moderate He background gas pressure was used to prepare PtAu thin films. The Pt bulk content was determined by neutron activation analysis, whereas X-ray diffraction and X-ray photoelectron spectroscopy were used to assess the bulk and the surface structure of the films, respectively. It is shown that metastable PtAu alloys with a unique fcc structure are formed over the whole composition range. The surface composition of the films closely follows the bulk content, and X-ray photoelectron spectroscopy reveals that the surface of the films is also made of a PtAu alloy. These films are stable under ambient conditions. The electrochemical properties of these films were determined by cyclic voltammetry in H 2 SO 4 electrolyte, and their reactivity toward the electrooxidation of CO and the electroreduction of O 2 was assessed. The CO stripping peak potential value increases with the Au content, indicating an increased binding energy in comparison with polycrystalline Pt. Similarly, there is a cathodic shift of the Pt oxide reduction peak for the Au-rich alloy that indicates stronger Pt-O binding energies as compared with Pt-rich alloy electrodes. At the surface, the presence of Au in close proximity to Pt atoms induces a shift of the d-band center of the Pt atoms that translates into stronger bonds with CO-and O-containing species at the surface of the samples. As far as we can tell, the surface composition and structure of the deposits are not modified following the electrochemical measurements.

Hydrazine (N2H4) is a promising high-power energy carrier for fuel cells, combining the energy density of methanol (MeOH) with the rapid oxidation kinetics of hydrogen (H2). N2H4 does not require expensive Pt group metals nor Au for low-potential (high voltage) oxidation, offering significantly lower fuel cell materials costs compared to H2, MeOH, ethanol (EtOH), and ammonia (NH3). In our study, we use rotating disk electrode (RDE) voltammetry to explore N2H4 oxidation at a wide variety of catalysts, including first-row transition metals (Co, Ni), coinage metals (Ag, Au) and Pt group metals (Ru, Rh, Pd, Ir, Pt). While several groups have focused on Co, Ni, or CoNi alloys, we find that other metals, including Ag, Ru, and Pd, offer much higher electron recovery and have more stable reactions, and still cost far less than Pt, Au, Rh, or Ir. We analyze our findings in terms of cost vs performance for the metals, developing a guide for the design of N2H4 fuel cell systems and sensors to suit various application spaces. The many metals studied also reveal an important trend for the theoretical understanding of catalysis: the onset and passivation of N2H4 oxidation in nearly every system were directly tied to the appearance or disappearance of specific metal surface states (e.g., hydrides and oxides). Indeed, metals with multiple surface states frequently showed multiple mechanisms for N2H4 oxidation, each with separate values for electron recovery. These observations provide support for the continued development of electrocatalytic theory in which different metal surface states are treated as independent materials with distinct reaction mechanisms.

Understanding of the NH 3 oxidation poisoning mechanism at Pt(100) is key to tackling a drawback of a reaction important to wastewater decontamination, electrochemical NH 3 sensors, and NH 3 fuel cells. Here we present a detailed study of poisoning adsorbates generated by NH 3 at Pt(100) thin films and identify new key species (1) by comparison to NO 2 − reduction adsorbates and (2) using literature FTIR and DEMS (differential electrochemical mass spectrometry) data. We show that NH 3 and NO 2 − generate identical intermediates at the same electrochemical potentials, suggesting that reactions as disparate as NH 3 oxidation and NO 2 − reduction follow a universal catalytic pathway for N-containing compounds at Pt(100). This represents a significant paradigm shift from 45 years of thought that suggested the two pathways were completely separate. We then use the behavior of poisoning, adsorbed intermediates to develop an in situ cleaning procedure that allows improvements in performance and lifetime for NH 3 electro-oxidation technologies. The in situ cleaning procedure, demonstrated for 1200 cleaning cycles over 2 h, required neither H 2 production nor Pt oxide formation. The latter trait allowed the employment of Pt(100) films without risk of immediate catalyst deorientation to a polycrystalline state. Article pubs.acs.org/JPCC