d-Orbital Electron Delocalization Realized by Axial Fe4 C Atomic Clusters Delivers High-Performance Fe-N-C Catalysts for Oxygen Reduction Reaction.

Fe-N-C catalyst for oxygen reduction reaction (ORR) has been considered as the most promising nonprecious metal catalyst due to its comparable catalytic performance to Pt in proton exchange membrane fuel cells (PEMFCs). The active centers of Fe-pyrrolic N4 have been proven to be extremely active for ORR. However, forming a stable Fe-pyrrolic N4 structure is a huge challenge. Here, a Cyan-Fe-N-C catalyst with Fe-pyrrolic N4 as the intrinsic active center is constructed with the help of axial Fe4 C atomic clusters, which shows a half-wave potential of up to 0.836 V (vs. RHE) in the acid environment. More remarkably, it delivers a high power density of 870 and 478 mW cm-2 at 1.0 bar in H2 -O2 and H2 -Air fuel cells, respectively. According to theoretical calculation and in situ spectroscopy, the axial Fe4 C can provide strong electronic perturbation to Fe-N4 active centers, leading to the d-orbital electron delocalization of Fe and forming the Fe-pyrrolic N4 bond with high charge distribution, which stabilizes the Fe-pyrrolic N4 structure and optimizes the OH* adsorption during the catalytic process. This work proposes a new strategy to adjust the electronic structure of single-atom catalysts based on the strong interaction between single atoms and atomic clusters.

Electrocatalysis Mechanism and Structure-Activity Relationship of Atomically Dispersed Metal-Nitrogen-Carbon Catalysts for Electrocatalytic Reactions.

Atomically dispersed metal-nitrogen-carbon catalysts (M-N-C) have been widely used in the field of energy conversion, which has already attracted a huge amount of attention. Due to their unsaturated d-band electronic structure of the center atoms, M-N-C catalysts can be applied in different electrocatalytic reactions by adjusting their own microscopic electronic structures to achieve the optimization of the structure-activity relationship. Consequently, it is of great significance for the revelation of electrocatalytic mechanism and structure-activity relationship of M-N-C catalysts. Thus, this review first introduces the relative research methods, including in situ/operando characterization techniques and theoretical calculation methods. Furthermore, clarifying the electrocatalytic mechanism and structure-activity relationship of M-N-C catalysts in different electrochemical energy conversion reactions is focused. Moreover, the future research directions are pointed out based on the discussion. This review will provide good guidance to systematically study the catalytic mechanism of single-atom catalysts and reasonably design the single-atom catalysts.

Kinetic Mechanisms and Emissions Investigation of Torrefied Pine Sawdust Utilized as Solid Fuel by Isothermal and Non-Isothermal Experiments.

This study comprehensively investigated the utilization of torrefied pine sawdust (PS) as solid fuels, involving the characterization of torrefied PS properties, the investigation of combustion behaviors and kinetic mechanisms by non-isothermal experiments, and the evaluation of emissions during isothermal experiments. Results show that torrefaction significantly improved the quality of the solids. The upgradation of torrefied PS properties then further enhanced its combustion performance. For the kinetics mechanisms, degradation mechanisms and diffusion mechanisms were respectively determined for the volatile combustion and the char combustion by using both Coats-Redfern (CR) and Freeman-Carroll (FC) methods. Further, after torrefaction, the emission of NO for volatile combustion reduced while it increased for char combustion. An inverse relationship was found between the conversion of fuel-N to NO and the nitrogen content in the torrefied samples. This study provided comprehensive insights for considering torrefaction as a pretreatment technique for PS utilization as a solid fuel.

Dechlorination of PVC wastes by hydrothermal treatment using alkaline additives.

Some chemicals were usually utilized in the hydrothermal dechlorination (HTD) of chlorine-containing wastes without revealing their roles. This work intends to investigate the role of chemical additives in the HTD of PVC (polyvinyl chloride). Several chemicals, including Na2CO3, KOH, NaOH, NH3·H2O, CaO and NaHCO3, were added into the PVC HTD process, which was conducted in subcritical Ni2+-containing water at 220°C for 30 min. The results show the alkalinity of additives had notable effects on the dechlorination efficiency (DE) of PVC due to the neutralization between HCl and additives. The most effective additive is Na2CO3, with the maximum DE of 65.12% at a Na2CO3 concentration of 0.025 M in this study. According to SEM, the hydrochar obtained from the HTD with Na2CO3 become more porous and looser than the others did, which contributed to the acceleration of PVC dechlorination. The DE vibration with the concentration of additives was different. For Na2CO3, it was firstly increased and then decreased with Na2CO3 concentration increasing from 0.01 to 0.04 M. For KOH and NaOH, it kept reducing with the concentration increasing from 0.02 to 0.08 M. The drop in DE was ascribed to surface poisoning and a loss in the supported active phase resulting from the formation of metal chloride species. FTIR analysis shows that the elimination of hydrogen chloride was the main route for HTD of PVC. All the results provide some fundamental data to find some cheap but efficient chemicals with aim to recycle the chlorinated organic wastes effectively.