Asymmetric Volcano Trend in Oxygen Reduction Activity of Pt and Non-Pt Catalysts: <i>In Situ</i> Identification of the Site-Blocking Effect

Proper understanding of the major limitations of current catalysts for oxygen reduction reaction (ORR) is essential for further advancement. Herein by studying representative Pt and non-Pt ORR catalysts with a wide range of redox potential (<i>E</i>_redox) via combined electrochemical, theoretical, and <i>in situ</i> spectroscopic methods, we demonstrate that the role of the site-blocking effect in limiting the ORR varies drastically depending on the <i>E</i>_redox of active sites; and the intrinsic activity of active sites with low <i>E</i>_redox have been markedly underestimated owing to the overlook of this effect. Accordingly, we establish a general asymmetric volcano trend in the ORR activity: the ORR of the catalysts on the overly high <i>E</i>_redox side of the volcano is limited by the intrinsic activity; whereas the ORR of the catalysts on the low <i>E</i>_redox side is limited by either the site-blocking effect and/or intrinsic activity depending on the <i>E</i>_redox

Monolayer Nickel Cobalt Hydroxyl Carbonate for High Performance All-Solid-State Asymmetric Supercapacitors

The emergence of atomically thick nanolayer materials, which feature a short ion diffusion channel and provide more exposed atoms in the electrochemical reactions, offers a promising occasion to optimize the performance of supercapacitors on the atomic level. In this work, a novel monolayer Ni–Co hydroxyl carbonate with an average thickness of 1.07 nm is synthesized via an ordinary one-pot hydrothermal route for the first time. This unique monolayer structure can efficiently rise up the exposed electroactive sites and facilitate the surface dependent electrochemical reaction processes, and thus results in outstanding specific capacitance of 2266 F g^–1. Based on this material, an all-solid-state asymmetric supercapacitor is developed adopting alkaline PVA (poly­(vinyl alcohol)) gel (PVA/KOH) as electrolyte, which performs remarkable cycling stability (no capacitance fade after 19 000 cycles) together with promising energy density of 50 Wh kg^–1 (202 μWh cm^–2) and high power density of 8.69 kW kg^–1 (35.1 mW cm^–2). This as-assembled all-solid-state asymmetric supercapacitor (AASC) holds great potential in the field of portable energy storage devices

Structure and Properties of Novel Cobalt-Free Oxides Nd_<i>x</i>Sr_1–<i>x</i>Fe_0.8Cu_0.2O_3−δ (0.3 ≤ <i>x</i> ≤ 0.7) as Cathodes of Intermediate Temperature Solid Oxide Fuel Cells

Novel cobalt-free perovskite oxides Nd_<i>x</i>Sr_1–<i>x</i>Fe_0.8Cu_0.2O_3−δ (NSFC<i>x</i>, 0.3 ≤ <i>x</i> ≤ 0.7) have been prepared and evaluated as cathodes for intermediate temperature solid oxide fuel cells (IT-SOFC). Their structure, thermal expansion, electric, and electrochemical properties are investigated. The oxides exhibit all cubic structure and show excellent thermal and electrochemical performance stability. The Nd content (<i>x</i>) significantly affects the properties of NSCF<i>x</i>. NSFC0.5 has been found to be the optimum composition with a peak electrical conductivity of 124 S cm^–1 at 700 °C, an average thermal expansion coefficient of 14.7 × 10^–6 K^–1 over 25–800 °C, a cathodic polarization resistance (<i>R</i>_p) of 0.071 Ω cm² at 700 °C, and a peak power density of 900 mW cm^–2 at 800 °C for samarium-doped ceria (SDC)-based single cells with NSFC<i>x</i> cathodes and Ni–SDC anodes. Moreover, no degradation has been observed for the <i>R</i>_p at 700 °C within 350 h. The concentration of surface oxygen vacancies and composition dependent crystallographic parameters have been found to be the dominating factors on performance of Nd_<i>x</i>Sr_1–<i>x</i>Fe_0.8Cu_0.2O_3−δ as IT-SOFC cathodes

Facile Spray Drying Route for the Three-Dimensional Graphene-Encapsulated Fe₂O₃ Nanoparticles for Lithium Ion Battery Anodes

Crumbled graphene sheet-wrapped nano-Fe₂O₃ (Fe₂O₃@GS) composites with a three-dimension (3D) hierarchical structure have been made by a facile and efficient spray drying route with a following mild heat reduction in air. In the as-obtained composites, the crumpled GS around Fe₂O₃ particles could not only provide a 3D conductive matrix but also buffer the volume change of Fe₂O₃. Fe₂O₃ particles which evenly distribute in the crumpled GS could also act as spacers to avoid the close restacking of GS. Compared to the bare Fe₂O₃, the Fe₂O₃@GS composites as Li ion battery anodes show dramatically improved electrochemical performance including cyclic stability and rate capability owing to the special encapsulated structure and the excellent synergistic effect between the two components

Tuning Nb–Pt Interactions To Facilitate Fuel Cell Electrocatalysis

High stability, availability of multiple oxidation states, and accessibility within a wide electrochemical window are the prime features of Nb that make it a favorable candidate for electrocatalysis, especially when it is combined with Pt. However, Nb has been used as a support in the form of oxides in all previously reported Pt–Nb electrocatalysts, and no Pt–Nb alloying phase has been demonstrated hitherto. Herein, we report a multifunctional Pt–Nb composite (PtNb/NbO_<i>x</i>-C) where Nb exists both as an alloying component with Pt and as an oxide support and is synthesized by means of a simple wet chemical method. In this work, the Pt–Nb alloy phase has been firmly verified with the help of multiple spectroscopic methods. This allows for the experimental evidence of the theoretical prediction that Pt–Nb alloy interactions improve the oxygen reduction reaction (ORR) activity of Pt. In addition, such a combination of multiphase Nb brings up myriad features encompassing increased ORR durability, immunity to phosphate anion poisoning, enhanced hydrogen oxidation reaction (HOR) activity, and oxidative carbon monoxide (CO) stripping, making this electrocatalyst useful in multiple fuel cell systems