Operando Electrodeposition of Nonprecious Metal Copper Nanocatalysts on Low-Dimensional Support Materials for Nitrate Reduction Reactions.

Supported nonprecious metal catalysts such as copper (Cu) are promising replacements for Pt-based catalysts for a wide range of energy-related electrochemical reactions. Direct electrochemical deposition is one of the most straightforward and versatile methods to synthesize supported nonprecious metal catalysts. However, further advancement in the design of supported nonprecious metal catalysts requires a detailed mechanistic understanding of the interplay between kinetics and thermodynamics of the deposition phenomena under realistic reaction conditions. Here, we study the electrodeposition of Cu on carbon nanotubes and graphene derivatives under electrochemical conditions using in situ liquid cell transmission electron microscopy (TEM). By combining real-time imaging, electrochemical measurements, X-ray photoelectron spectroscopy (XPS), and finite-element analysis (FEA), we show that low-dimensional support materials, especially carbon nanotubes, are excellent for generating uniform and finely dispersed platinum group metal-(PGM)-free catalysts under mild electrochemical conditions. The electrodeposited Cu on graphene and carbon nanotubes is also observed to show good electrochemical activity toward nitrate reduction reactions (NO3RRs), further supported by density functional theory (DFT) calculations. Nitrogen doping plays an important role in guiding nonprecious metal deposition, but its low electrical conductivity may give rise to lower NO3RR activity compared to its nondoped analogue. The development of supported nonprecious metals through interfacial and surface engineering for the design of supported catalysts will substantially reduce the demand for precious metals and generate robust catalysts with better durability, thereby presenting opportunities for solving the critical problems in energy storage and electrocatalysis.

[Source Apportionment and Pollution Assessment of Soil Heavy Metal Pollution Using PMF and RF Model: A Case Study of a Typical Industrial Park in Northwest China].

Based on the concentration data of seven heavy metal elements[As, Cd, Cu, Pb, Hg, Ni, and Cr(Ⅵ)] in the surface soil of a typical industrial park in northwest China, the characteristics of heavy metal pollution in the industrial park were analyzed, and the ecological risk and pollution were evaluated using the potential ecological risk index and the index of geo-accumulation. The positive matrix factorization (PMF) model and random forest (RF) model were used for quantitative source analysis, and the emission data of sampling enterprises and empirical data of the source emission component spectrum were combined to identify the characteristic elements and determine the emission source category. The results showed that the heavy metals at all sampling points in the park did not exceed the second-class screening value of construction land in the soil pollution risk control standard for construction land (GB 36600-2018). However, compared with the local soil background values, five elements, excluding As and Cr, were enriched in different degrees, presenting slight pollution and moderate ecological risk (RI=250.04). Cd and Hg were the main risk elements of the park. The results of source analysis showed that the five main sources of pollution were fossil fuel combustion and chemical production sources (33.73%, 9.71%, total source contribution rate of PMF and RF, respectively; the same below), natural sources and waste residue landfill (32.40%, 40.80%), traffic emissions (24.49%, 48.08%), coal burning and non-ferrous metal smelting (5.43%, 0.11%), and electroplating and ore smelting (3.95%, 1.30%). The simulation R2 of the total variable of the two models were above 0.96, indicating that the models could predict heavy metals well. However, considering the actual situation of the number of enterprises in the park and roading density, the main pollution sources of soil heavy metals in the park should be industrial sources, and the simulation results of the PMF model were closer to the actual situation in the park.

Iron carbide nanoparticles supported on an N-doped carbon porous framework as a bifunctional material for electrocatalytic oxygen reduction and supercapacitors.

Highly active and durable bifunctional materials are of pivotal importance for energy conversion and storage devices, yet a comprehensive understanding of their geometric and electronic influence on electrochemical activity is urgently needed. Fe-N-C materials with physical and chemical structural merits are considered as one of the promising candidates for efficient oxygen reduction reaction electrocatalysts and supercapacitor electrodes. Herein, Fe3C nanoparticles supported on a porous N-doped carbon framework (denoted as Fe3C/PNCF) were readily prepared by one-step chemical vapor deposition under the assistance of a NaCl salt template. The experiment results revealed that the as-synthesized Fe3C/PNCF nanocomposites successfully displayed attractive electrocatalytic oxygen reduction reaction (ORR) activity comparable to that of the Pt/C catalyst (E1/2 of 0.84 V and 0.83 V, respectively), and a superior capacitance of 385.3 F g-1 under 1 A g-1 for a supercapacitor. It's proposed that the increased pyridinic and graphitic N coordination on the hydrophilic porous framework provides more electrochemical active surface area for the storage and transport of electrolyte ions. Additionally, an appropriate d-band center created by the optimized adsorption function endows Fe3C/PNCF with excellent electrochemical properties. The results confirmed that the integration strategy of porous heterogeneous structure and accessible active sites balanced the complex relationship between geometry, electronic structure, and electrochemical activity. Our research provides a facile approach for fabricating multi-functional nanomaterials applicable in both ORR and supercapacitors in the future.