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The operating principle of a Pt thin-film H2 gas sensor was investigated using a combination of surface sensitive ambient-pressure X-ray photoelectron spectroscopy and bulk sensitive X-ray absorption fine structure techniques, which provided chemical and structure information under working conditions, coupled with electric resistivity measurements. It is shown that the sensor response was in a linear relation with both coverages of H and O atoms on the Pt surface. Moreover, the bulk structure of Pt remains unchanged under H2 exposure. These observations support that the resistivity change is associated with electron scattering in the near-surface region. [ABSTRACT FROM AUTHOR]

We developed a 3D electrochemical model for simulating the electrochemical properties and revealing the internal properties of a single LiFePO 4 secondary particle during cycling. The main model parameters, such as the diffusion coefficient and rate constant, were optimized using rate capability data, which have been measured experimentally with a unique single particle measurement technique. We simulated voltage profiles at different c-rates from 2 to 20C, which were approximately equivalent to the experimental voltage profiles. The model estimated real-time overpotential, lithium ion concentration, and state-of-charge within the single particle, which have not been obtained experimentally, while changing design parameters and operating conditions. We validated the reliability and applicability of the model by comparing and analyzing the electrochemical results of various LiFePO 4 secondary particles with variable design parameters (i.e., solid volume fraction, secondary particle size, and primary particle size). This graphics illustrates a 24 μm LiFePO4 secondary particle consisting of millions of primary particles of 100–200 nm in diameter. We propose a 3D electrochemical model for simulating the electrochemical properties and unveiling the internal properties of the single particle while changing both particle design parameters and operating conditions. Image 1 • A single LiFePO 4 secondary particle shows high capacity retention at high C-rate. • The particle was modeled with reflecting the experimental conditions. • Performance can be easily predicted by different design parameters using simulation tool. • Internal properties of a single particle were observed, which cannot be measured by experimental methods. [ABSTRACT FROM AUTHOR]

Identifying the active sites and their dynamic changes is of critical significance for designing efficient oxygen evolution reaction (OER) catalysts, but remains challenging owing to the complexity in structure and reaction process. Herein, using various operando characterizations, we identify the origin of a 12-time enhancement of OER activity over pure cobalt oxyhydroxide achieved by confining high-valance chromium into its lattice. Operando X-ray absorption spectroscopy reveals in-situ generation of high-valence Cr state with shortened Cr O bond relative to original state, indicating potential-dependent formation of OER intermediates on Cr sites. Operando electrochemical impedance and infrared spectroscopy provide direct spectroscopic evidence of OOH* on Cr site. Combined with theoretical calculations, the confined Cr is identified as the active site with improved bonding strength with O*, exhibiting a lower overpotential than that on Co site. This study elucidates the dynamic behaviour of active sites and provides guiding for improving OER catalysts via introducing high-valance metals. Layered cobalt oxyhydroxide showed a 12-fold OER activity enhancement after confining chromium. Various operando characterizations revealed the potential-relevant electronic and structural dynamics of Co and Cr under realistic working conditions, identifying that high-valence Cr is the active site with moderate bond strength with reaction intermediates. [Display omitted] • The origin of a 12-time OER activity enhancement is identified by various operando characterizations. • Operando electrochemical impedance and X-ray absorption spectroscopy reveal the dynamic evolutions of the Co and Cr sites. • Operando infrared spectroscopy provide direct spectroscopic evidence of OOH* intermediates on Cr site. • High-valence Cr is identified as the active site with moderate bond strength with reaction intermediates. [ABSTRACT FROM AUTHOR]