Wenhui He

Abstract Electrocatalytic recycling of waste nitrate (NO 3 − ) to valuable ammonia (NH 3 ) at ambient conditions is a green and appealing alternative to the Haber−Bosch process. However, the reaction requires multi-step electron and proton transfer, making it a grand challenge to drive high-rate NH 3 synthesis in an energy-efficient way. Herein, we present a design concept of tandem catalysts, which involves coupling intermediate phases of different transition metals, existing at low applied overpotentials, as cooperative active sites that enable cascade NO 3 − -to-NH 3 conversion, in turn avoiding the generally encountered scaling relations. We implement the concept by electrochemical transformation of Cu−Co binary sulfides into potential-dependent core−shell Cu/CuO x and Co/CoO phases. Electrochemical evaluation, kinetic studies, and in−situ Raman spectra reveal that the inner Cu/CuO x phases preferentially catalyze NO 3 − reduction to NO 2 − , which is rapidly reduced to NH 3 at the nearby Co/CoO shell. This unique tandem catalyst system leads to a NO 3 − -to-NH 3 Faradaic efficiency of 93.3 ± 2.1% in a wide range of NO 3 − concentrations at pH 13, a high NH 3 yield rate of 1.17 mmol cm −2 h −1 in 0.1 M NO 3 − at −0.175 V vs. RHE, and a half-cell energy efficiency of ~36%, surpassing most previous reports.

Nitrogen-doped species (NDs) are theoretically accepted as a determinant of the catalytic activity of metal-free N-doped carbon (NC) catalysts for oxygen reduction reaction (ORR). However, direct relationships between ND type and ORR activity have been difficult to extract because the complexity of carbon matrix impairs efforts to expose specific NDs. Herein, we demonstrate the fabrication of a 3D hierarchically porous NC catalyst with micro-, meso-, and macroporosity in one structure, in which sufficient exposure and availability of inner-pore catalytic sites can be achieved due to its super-high surface area (2191 cm(2) g(-1) ) and interconnected pore system. More importantly, in-situ formation of graphitic-N species (GNs) on the surface of NC stimulated by KOH activation enables us to experimentally reveal the catalytic nature of GNs for ORR, which is of great significance for the design and development of advanced metal-free NC electrocatalysts.

This paper presents a study to introduce and experimentally validate an innovative concrete filled steel tubular (CFT) column system, named as confined CFT or CCFT, for improved seismic design of steel and concrete composite structures. Based on fundamental mechanics, the concept is aimed at controlling the local buckling of the steel tube and confining the concrete in the potential plastic hinge regions of a CFT column. To achieve this, several efficient details of transverse confinement are proposed. In the first phase of the study, carbon-fiber-reinforced plastic as additional confinement of CCFT columns was examined through experimental testing. As demonstrated from the results of axial compression tests and seismic loading tests, the new type of CFT column system can provide excellent seismic performance. The complicated local buckling and confinement mechanisms were examined using a proposed simple analytical model.

Developing non-precious metal electrocatalysts (NPMCs) for the oxygen reduction reaction (ORR) is of paramount importance for commercial implementation of several clean energy techniques (e.g. proton exchange membrane fuel cells). However, limited understanding of the ORR catalytic mechanism of NPMCs greatly hinders the progress in the precise fabrication of NPMCs at the molecular or atomic level. Recently, an increasing number of studies have demonstrated the crucial role of a carbon matrix in exposing, stabilizing, and activating the catalytic sites, thus providing a platform to identify the nature of NPMCs. Herein, the unique structural effects of a carbon matrix in NPMCs are first reviewed to inspire the development of more advanced NPMCs for the ORR.