No abstract

Carbon material is considered a promising electrocatalyst for the CO2 reduction reaction (CO2RR); especially, N-doped carbon material shows high CO Faradic efficiency (FECO) when using pyridinic N species as the active site. However, in the past decade, more efforts were focused on the preparation of various carbon nanostructures containing abundant pyridinic N species and few researchers studied the electronic structure modulation of the pyridinic N site. The curvature of the carbon substrate is an easily controllable parameter for modulating the local electronic environment of catalytic sites. In this research, carbon nanotubes (CNTs) with different diameters are applied to modulate the electronic environment of pyridinic N by the curvature effect. The pyridinic N sites doped on CNTs with the average curvature of 0.04 show almost 100% FECO at the current density of 3 mA cm–2 at −0.6 V vs RHE and 91% FECO retention after 12 h test, which is superior to most of the carbon-based electrocatalysts. As demonstrated by density functional theory simulation, the pyridinic N site forms a strong local electric field around the nearby C active site and protrudes out of the curved CNT surface like a tip, which remarkably enriches the protons around the adsorbed CO2 molecule.

In this study, the effects of torrefaction pretreatment on physicochemical characteristics and pyrolysis behavior of cornstalk were investigated based on the changes in its chemical and structural characteristics. The results indicated that torrefaction treatment improved the fuel properties with elevated torrefaction temperature, including the lower volatile content, higher carbon content, and higher heating value. In addition, serious torrefaction promoted complete degradation of hemicellulose, while the lignin was increased obviously. The crystallinity degree of cornstalk increased first and then reduced with the torrefaction temperature. Slight torrefaction enhanced the devolatilization and thermochemical reactivity of cornstalk, but serious torrefaction discouraged the volatile release. Kinetic parameter analysis indicated that the Ozawa–Flynn–Wall model was more accurate in calculating the activation energy, and the average activation energy gradually increased from 196.06 to 199.21, 203.17, and 217.58 kJ/mol. Furthermore, the thermodynamic parameters also showed an increasing trend with elevated torrefaction temperature. These results provide important basic data support for the thermochemical conversion of cornstalk to energy and chemicals.