Oxidation Evolution and Activity Origin of N-Doped Carbon in the Oxygen Reduction Reaction

N-doped carbon materials,with their applications as electrocatalysts for the oxygen reduction reaction(ORR),have been extensively studied.However,a negletcted fact is that the operating potential of the ORR is higher than the theoretical oxida-tion potential of carbon,possibly leading to the oxidation of carbon materials.Consequently,the infl uence of the structural oxidation evolution on ORR performance and the real active sites are not clear.In this study,we discover a two-step oxida-tion process of N-doped carbon during the ORR.The fi rst oxidation process is caused by the applied potential and bubbling oxygen during the ORR,leading to the oxidative dissolution of N and the formation of abundant oxygen-containing functional groups.This oxidation process also converts the reaction path from the four-electron(4e)ORR to the two-electron(2e)ORR.Subsequently,the enhanced 2e ORR generates oxidative H_(2)O_(2),which initiates the second stage of oxidation to some newly formed oxygen-containing functional groups,such as quinones to dicarboxyls,further diversifying the oxygen-containing functional groups and making carboxyl groups as the dominant species.We also reveal the synergistic eff ect of multiple oxygen-containing functional groups by providing additional opportunities to access active sites with optimized adsorption of OOH*,thus leading to high effi ciency and durability in electrocatalytic H_(2)O_(2) production.

Engineering Ru(IV)charge density in Ru@RuO2 core-shell electrocatalyst via tensile strain for efficient oxygen evolution in acidic media

The design of efficient Ru-based electrocatalysts with high intrinsic activities for acidic water oxidation is highly desirable and challenging for water splitting in proton exchange membrane electrolyzers.Here,for the first time,we engineer the charge density of Ru(IV)by creating tensile strains in the RuO2 shell of Ru@RuO2 core-shell nanoparticles,viz.Ru@RuO2-L.High-resolution spectroscopic characterizations confirm the presence of av.6%tensile strain in Ru-O bonds,which results in an effective reduction of the Ru(IV)charge density.The resultant Ru^X+(4<X<5)active sites greatly accelerate the oxygen evolution reaction(OER)in an acidic electrolyte,leading to a remarkably low overpotential of 191 mV at 10 mA cm^-2.These values are lower than those for the benchmark RuO2 catalyst and are also among the lowest for efficient Ru-based electrocatalysts reported thus far.The specific activity and mass activity are also greatly enhanced 4.2-fold and 17.7-fold compared to those of RuO2,respectively.The acidic OER activity improvement is ascribed to the lowered adsorption energy of*OOH,owing to the reduced charge density of Ru(IV),and the rapid charge transport owing to the Ru core.Ru@RuO2-L also demonstrates high feasibility as the anode catalyst for the overall water splitting in acidic media.

Dual-site collaboration boosts electrochemical nitrogen reduction on Ru-S-C single-atom catalyst

Electrocatalytic reduction of nitrogen into ammonia(NH_(3))is a highly attractive but challenging route for NH_(3)production.We propose to realize a synergetic work of multi reaction sites to overcome the limitation of sustainable NH_(3)production.Herein,using ruthenium-sulfur-carbon(Ru-S-C)catalyst as a prototype,we show that the Ru/S dual-site cooperates to catalyse eletrocatalytic nitrogen reduction reaction(eNRR)at ambient conditions.With the combination of theoretical calculations,in situ Raman spectroscopy,and experimental observation,we demonstrate that such Ru/S dual-site cooperation greatly facilitates the activation and first protonation of N_(2)in the rate-determining step of eNRR.As a result,Ru-S-C catalyst exhibits significantly enhanced eNRR performance compared with the routine Ru-N-C catalyst via a single-site catalytic mechanism.We anticipate that our specifically designed dual-site collaborative catalytic mechanism will open up a new way to offers new opportunities for advancing sustainable NH_(3)production.

A Robust Gaussian Mixture Model for Mobile Robots’ Vision-based Pose Estimation

In dynamic environments, the moving landmarks can make the accuracy of traditional vision-based pose estimation worse or even failure. To solve this problem, a robust Gaussian mixture model for vision-based pose estimation is proposed. The motion index is added to the traditional graph-based vision-based pose estimation model to describe landmarks’ moving probability, transforming the classic Gaussian model to Gaussian mixture model, which can reduce the influence of moving landmarks for optimization results. To improve the algorithm’s robustness to noise, the covariance inflation model is employed in residual equations. The expectation maximization method for solving the Gaussian mixture problem is derived in detail, transforming the problem into classic iterative least square problem. Experimental results demonstrate that in dynamic environments, the proposed method outperforms the traditional method both in absolute accuracy and relative accuracy, while maintains high accuracy in static environments. The proposed method can effectively reduce the influence of the moving landmarks in dynamic environments, which is more suitable for the autonomous localization of mobile robots.

Hydrogen-assisted activation of N_(2)molecules on atomic steps of ZnSe nanorods

Electrochemical reduction reaction of nitrogen(NRR)offers a promising pathway to produce ammonia(NH_(3))from renewable energy.However,the development of such process has been hindered by the chemical inertness of N_(2).It is recently proposed that hydrogen species formed on the surface of electrocatalysts can greatly enhance NRR.However,there is still a lack of atomiclevel connection between the hydrogenation behavior of electrocatalysts and their NRR performance.Here,we report an atomistic understanding of the hydrogenation behavior of a highly twinned ZnSe(T-ZnSe)nanorod with a large density of surface atomic steps and the activation of N_(2)molecules adsorbed on its surface.Our theoretical calculations and in situ infrared spectroscopic characterizations suggest that the atomic steps are essential for the hydrogenation of T-ZnSe,which greatly reduces its work function and efficiently activates adsorbed N_(2)molecules.Moreover,the liquid-like and free water over T-ZnSe promotes its hydrogenation.As a result,T-ZnSe nanorods exhibit significantly enhanced Faradaic efficiency and NH3 production rate compared with the pristine ZnSe nanorod.This work paves a promising way for engineering electrocatalysts for green and sustainable NH3 production.

Dynamically modulated synthesis of hollow metal-organic frameworks for selective hydrogenation reactions

Hollow metal-organic frameworks(MOFs)have attracted increasing attention in the field of catalysis in recent years due to their unique cavity structure with fast mass-diffusion rates and easily accessible active sites.Here,we report the use of dynamic modulators,which are formed by the in-situ imine condensation reaction of 4-aminobenzoic acid and 4-formylbenzoic acid,to regulate the growth of MOFs to synthesize well-defined hollow thioether functionalized UiO-67(denoted as H-UiO-67-S)single crystals.After supporting Pd nanoparticles,the designed catalysts Pd@H-UiO-67-S show excellent conversion(>99.9%),selectivity(>99.9%),and stability(10 cycles)in the selective hydrogenation of nitrobenzenes with other reducible groups.Density functional theory calculations and the experimental results reveal that Pd nanoparticles not only selectively adsorb the nitro-groups on nitrobenzene,but also restrict the adsorption of the aniline product,due to the interaction of thioether with Pd in the confined pores of H-UiO-67-S,finally result in a significant increase in selectivity of nitro-hydrogenation.

Electrosynthesis of hydroxylamine from nitrate reduction in water

Hydroxylamine(NH_(2)OH),a vital but unstable industrial feedstock,is presently prepared under harsh conditions that cause environmental and energy concerns.Here,we report an electrochemical method to prepare oximes,which serve as precursors for NH_(2)OH after facile hydrolysis.The carbon-supported amorphous Mn electrocatalyst delivers a current density of~100 mA cm^(-2) with a Faradaic efficiency of 40.92%and a yield rate of 0.251 mmol cm^(-2)h^(-1) for formaldoxime(CH_(2)NOH)generation by using nitrate and formaldehyde as reactants.Formaldoxime can be easily released to produce NH_(2)OH via hydrolysis.Impressively,this method exhibits an economic advantage over conventional manufacturing based on techno-economic analysis.A series of control experiments,in situ characterizations,and theoretical simulations unveil the reaction mechanism via the spontaneous reaction between an aldehyde and*NH_(2)OH intermediate derived from nitrate electroreduction.The high activity of Mn originates from its inhibitory effects on the further reduction of key*NH_(2)OH intermediate.This strategy opens a sustainable and green way for NH_(2)OH synthesis under mild conditions using renewable energy.