The voltage reversal of water electrolyzers and fuel cells induces a large positive potential on the hydrogen electrodes, followed by severe system degradation. Applying a reversible multifunctional electrocatalyst to the hydrogen electrode is a practical solution. Ir exhibits excellent catalytic activity for hydrogen evolution reactions (HER), and hydrogen oxidation reactions (HOR), yet irreversibly converts to amorphous IrO_x at potentials > 0.8 V/RHE, which is an excellent catalyst for oxygen evolution reactions (OER), yet a poor HER and HOR catalyst. Harnessing the multifunctional catalytic characteristics of Ir, here we design a unique Ir-based electrocatalyst with high crystallinity for OER, HER, and HOR. Under OER operation, the crystalline nanoparticle generates an atomically-thin IrO_x layer, which reversibly transforms into a metallic Ir at more cathodic potentials, restoring high activity for HER and HOR. Our analysis reveals that a metallic Ir subsurface under thin IrO_x layer can act as a catalytic substrate for the reduction of Ir ions, creating reversibility. Our work not only uncovers fundamental, uniquely reversible catalytic properties of nanoparticle catalysts, but also offers insights into nanocatalyst design.

In this paper a new multi-view/3D human action/interaction database is presented. The database has been created using a convergent eight camera setup to produce high definition multi-view videos, where each video depicts one of eight persons performing one of twelve different human motions. Various types of motions have been recorded, i.e., scenes where one person performs a specific movement, scenes where a person executes different movements in a succession and scenes where two persons interact with each other. Moreover, the subjects have different body sizes, clothing and are of different sex, nationalities, etc.. The multi-view videos have been further processed to produce a 3D mesh at each frame describing the respective 3D human body surface. To increase the applicability of the database, for each person a multi-view video depicting the person performing sequentially the six basic facial expressions separated by the neutral expression has also been recorded. The database is freely available for research purposes.

A novel method for preparing nitrogen-doped graphite felts as positive electrodes in vanadium redox flow batteries was developed and studied. These materials were synthesized by directly coating a thin polypyrrole layer on the graphite felt surface followed by subsequent carbonization in the presence of Co (NGF-Co). Co played an important role in promoting the concentration of nitrogen functional groups that are active towards the VO²⁺/VO₂ ⁺ redox couple. The physical and electrochemical properties of the nitrogen-doped carbons were characterized by X-ray photoelectron spectrometry, cyclic voltammetry, impedance spectroscopy and charge–discharge tests. These results indicate that synthesizing NGF-Co via this facile method substantially improved the electrochemical catalytic activity and reduced charge transfer resistance. It exhibited a 211% and 34% increase in discharge capacity over the pristine graphite felt and thermally oxidized graphite felt, respectively, at a high current density of 150 mA cm⁻². The enhanced performance was attributed to the abundant active nitrogen groups created on the graphite felt, which benefit the fast electrochemical kinetics of vanadium redox reactions.

Herein, we introduce a simple method to prepare hierarchical graphene with a tunable pore structure by activating graphene oxide (GO) with a two-step thermal annealing process. First, GO was treated at 600 °C by rapid thermal annealing in air, followed by subsequent thermal annealing in N₂. The prepared graphene powder comprised abundant slit nanopores and micropores, showing a large specific surface area of 653.2 m²/g with a microporous surface area of 367.2 m²/g under optimized conditions. The pore structure was easily tunable by controlling the oxidation degree of GO and by the second annealing process. When the graphene powder was used as the supercapacitor electrode, a specific capacitance of 372.1 F/g was achieved at 0.5 A/g in 1 M H₂SO₄ electrolyte, which is a significantly enhanced value compared to that obtained using activated carbon and commercial reduced GO. The performance of the supercapacitor was highly stable, showing 103.8% retention of specific capacitance after 10,000 cycles at 10 A/g. The influence of pore structure on the supercapacitor performance was systematically investigated by varying the ratio of micro- and external surface areas of graphene.