Oxidatively induced exposure of active surface area during microwave assisted formation of Pt3Co nanoparticles for oxygen reduction reaction.

The oxygen reduction reaction (ORR), the rate-limiting reaction in proton exchange membrane fuel cells, can efficiently be facilitated by properly manufactured platinum catalysts alloyed with late 3d transition metals. Herein we synthesize a platinum : cobalt nanoparticulate catalyst with a 3 : 1 atomic ratio by reduction of a dry metalorganic precursor blend within a commercial household microwave oven. The formed nanoparticles are simultaneously anchored to a carbon black support that enables large Pt surface area. Two separate microwave treatment steps were employed, where step one constitutes a fast oxidative treatment for revealing active surface area while a reductive secondary annealing treatment promotes a Pt rich surface. The resulting Pt3Co/C catalyst (∼3.4 nm) demonstrates an enhanced ORR activity directly attributed to incorporated Co with a specific and mass activity of 704 µA cmPt -2 and 352 A gPt -1 corresponding to an increase by 279% and 66% respectively compared to a commercial Pt/C (∼1.8 nm) catalyst measured under identical conditions. The method's simplicity, scalability and novelty is expected to further assist in Pt-Co development and bring the catalyst one step closer toward commercialization and utility in fuel cells.

Influence of Sb5+ as a Double Donor on Hematite (Fe3+) Photoanodes for Surface-Enhanced Photoelectrochemical Water Oxidation.

To exploit the full potential of hematite (α-Fe2O3) as an efficient photoanode for water oxidation, the redox processes occurring at the Fe2O3/electrolyte interface need to be studied in greater detail. Ex situ doping is an excellent technique to introduce dopants onto the photoanode surface and to modify the photoanode/electrolyte interface. In this context, we selected antimony (Sb5+) as the ex situ dopant because it is an effective electron donor and reduces recombination effects and concurrently utilize the possibility to tuning the surface charge and wettability. In the presence of Sb5+ states in Sb-doped Fe2O3 photoanodes, as confirmed by X-ray photoelectron spectroscopy, we observed a 10-fold increase in carrier concentration (1.1 × 1020 vs 1.3 × 1019 cm-3) and decreased photoanode/electrolyte charge transfer resistance (∼990 vs ∼3700 Ω). Furthermore, a broad range of surface characterization techniques such as Fourier-transform infrared spectroscopy, ζ-potential, and contact angle measurements reveal that changes in the surface hydroxyl groups following the ex situ doping also have an effect on the water splitting capability. Theoretical calculations suggest that Sb5+ can activate multiple Fe3+ ions simultaneously, in addition to increasing the surface charge and enhancing the electron/hole transport properties. To a greater extent, the Sb5+- surface-doped determines the interfacial properties of electrochemical charge transfer, leading to an efficient water oxidation mechanism.

Fabrication of microporous layer - free hierarchical gas diffusion electrode as a low Pt-loading PEMFC cathode by direct growth of helical carbon nanofibers.

Improving interfacial contact between each component in the proton exchange membrane fuel cell (PEMFC) can lead to a significant increase in power density and Pt utilization. In this work, the junction between the catalyst layer and gas diffusion layer (GDL) is greatly enhanced through direct attachment of helical carbon nanofibers, giving rise to a hierarchical structure within the electrical interconnections. The alternative novel GDL is produced by spraying a thin layer of Pd2C60 precursor on commercial carbon paper, followed by chemical vapor deposition growth resulting in a surface morphology of well-attached nanofibers surrounding the microfibers present in the commercial carbon paper. Subsequent solvothermal deposition of platinum nanoparticles allowed evaluation of its suitability as gas diffusion electrode in cathodic H2/O2 PEMFC environment. A combination of lowered charge transfer resistance and enhanced Pt-utilization is attributed to its unique wire-like appearance and its robust properties. The fabricated microporous layer - free GDL is suitable for relatively aggressive membrane electrode assembly fabrication procedures and is produced by industrially favorable techniques, rendering it capable of efficiently supporting small amounts of precious metal catalyst nanoparticles in various PEM applications.

Cationic Vacancy Defects in Iron Phosphide: A Promising Route toward Efficient and Stable Hydrogen Evolution by Electrochemical Water Splitting.

Engineering the electronic properties of transition metal phosphides has shown great effectiveness in improving their intrinsic catalytic activity for the hydrogen evolution reaction (HER) in water splitting applications. Herein, we report for the first time, the creation of Fe vacancies as an approach to modulate the electronic structure of iron phosphide (FeP). The Fe vacancies were produced by chemical leaching of Mg that was introduced into FeP as "sacrificial dopant". The obtained Fevacancy-rich FeP nanoparticulate films, which were deposited on Ti foil, show excellent HER activity compared to pristine FeP and Mg-doped FeP, achieving a current density of 10 mA cm-2 at overpotentials of 108 mV in 1 m KOH and 65 mV in 0.5 m H2 SO4 , with a near-100 % Faradaic efficiency. Our theoretical and experimental analyses reveal that the improved HER activity originates from the presence of Fe vacancies, which lead to a synergistic modulation of the structural and electronic properties that result in a near-optimal hydrogen adsorption free energy and enhanced proton trapping. The success in catalytic improvement through the introduction of cationic vacancy defects has not only demonstrated the potential of Fe-vacancy-rich FeP as highly efficient, earth abundant HER catalyst, but also opens up an exciting pathway for activating other promising catalysts for electrochemical water splitting.

Robust hierarchical 3D carbon foam electrode for efficient water electrolysis.

Herein we report a 3D heterostructure comprising a hierarchical macroporous carbon foam that incorporates mesoporous carbon nanotubes decorated with cobalt oxide nanoparticles as an unique and highly efficient electrode material for the oxygen evolution reaction (OER) in electrocatalytic water splitting. The best performing electrode material showed high stability after 10 h, at constant potential of 1.7 V vs. RHE (reversible hydrogen electrode) in a 0.1 M KOH solution and high electrocatalytic activity in OER with low overpotential (0.38 V vs RHE at 10 mA cm-2). The excellent electrocatalytic performance of the electrode is rationalized by the overall 3D macroporous structure and with the firmly integrated CNTs directly grown on the foam, resulting in a large specific surface area, good electrical conductivity, as well as an efficient electrolyte transport into the whole electrode matrix concurrent with an ability to quickly dispose oxygen bubbles into the electrolyte. The eminent properties of the three-dimensional structured carbon matrix, which can be synthesized through a simple, scalable and cost effective pyrolysis process show that it has potential to be implemented in large-scale water electrolysis systems.

Comprehensive Study of an Earth-Abundant Bifunctional 3D Electrode for Efficient Water Electrolysis in Alkaline Medium.

We report efficient electrolysis of both water-splitting half reactions in the same medium by a bifunctional 3D electrode comprising Co3O4 nanospheres nucleated on the surface of nitrogen-doped carbon nanotubes (NCNTs) that in turn are grown on conductive carbon paper (CP). The resulting electrode exhibits high stability and large electrochemical activity for both oxygen and hydrogen evolution reactions (OER and HER). We obtain a current density of 10 mA/cm(2) in 0.1 M KOH solution at overpotentials of only 0.47 and 0.38 V for OER and HER, respectively. Additionally, the experimental observations are understood and supported by analyzing the Co3O4:NCNT and NCNT:CP interfaces by ab initio calculations. Both the experimental and the theoretical studies indicate that firm and well-established interfaces along the electrode play a crucial role on the stability and electrochemical activity for both OER and HER.