Low-coordinated Ni-N_(1)-C_(3)sites atomically dispersed on hollow carbon nanotubes for efficient CO_(2)reduction

Low-coordinated single atom catalysts compared to M-N4 are appealing in optimized electronic structure for CO_(2)electroreduction,but the preparation is still very challenging.Herein,a novel single Ni atom catalyst with Ni-N_(1)-C_(3)configuration is in-situ evolved on curved carbon nanotubes.The obtained Ni-N_(1)-C_(3)catalyst exhibits a superior CO Faradaic efficiency of 97%and turnover frequency of 2,890 h^(−1)at−0.9 V versus the reversible hydrogen electrode,as well as long-term stability over 45 h.High current densities exceeding 200 mA·cm^(−2)and CO Faradaic efficiency of 99%are achieved in flow-cell.Moreover,in-situ potentialand time-dependent Raman spectra identify the key intermediates of*COOH and*CO during CO_(2)-to-CO conversion.Theoretical calculations reveal that the upward-shifted d-band center and charge-rich Ni sites of Ni-N_(1)-C_(3)facilitate the electron transfer to*COOH and thus reduce the*COOH formation energy barrier.This work demonstrates a strategy for modulating the coordination environment for efficient CO_(2)reduction.

Low-coordinated surface sites make truncated Pd tetrahedrons as robust ORR electrocatalysts outperforming Pt for DMFC devices

Developing highly stable and active non-Pt oxygen reduction reaction(ORR)electrocatalysts for power generation device raises great concerns and remains a challenge.Here,we report novel truncated Pd tetrahedrons(T-Pd-Ths)enclosed by{111}facets with excellent uniformity,which have both low-coordinated surface sites and distinct lattice distortions that would induce“local strain”.In alkaline electrolyte,the T-Pd-Ths/C achieves remarkable ORR specific/mass activity(SA/MA)of 2.46 mA·cm^(−2)/1.69 A·mgPd^(−1),which is 12.3/16.9 and 10.7/14.1 times higher than commercial Pd/C and Pt/C,respectively.The T-Pd-Ths/C also exhibits high in-situ carbon monoxide(CO)tolerance and 50,000 cycles durability with an activity loss of 7.69%and morphological stability.The rotating ring-disk electrode(RRDE)measurements show that a 4-electron process occurs on T-PdThs/C.Theoretical calculations demonstrate that the low-coordinated surface sites contribute largely to the enhancement of ORR activity.In actual direct methanol fuel cell(DMFC)device,the T-Pd-Ths/C delivers superior open-circuit voltage(OCV)and peak power density(PPD)to commercial Pt/C from 25 to 80℃,and the maximum PPD can reach up to 163.7 mW·cm−2.This study demonstrates that the T-Pd-Ths/C holds promise as alternatives to Pt for ORR in DMFC device.

Assembling High-Temperature Single-Molecule Magnets with Low-Coordinate Bis(amido)Dysprosium Unit[DyN_(2)]^(+)via Cl-K-Cl Linkage

Symmetryandaxialityarethought tobeguides toward the pursuit of high energy barrier and blocking temperature for thedysprosium(Ⅲ)(Dy^(Ⅲ))single-molecule magnets(SMMs).The Dy^(Ⅲ)complexeswith low coordination numbers are intended to satisfy axial symmetry.Here,we report four four-coordinate Dy^(Ⅲ)SMMs based on bis(arylamido)dysprosium building block{Dy(N^(RR’))2(μ-Cl)_(2)K}(N^(RR’)={N(SiMe_(3))(C_(6)H_(3)iPr_(2)-2,6)}^(−)),with two strong Dy–N and twoweak Dy–Cl bonds.Through fine-tuning of axial anisotropy,the SMM with the largest N–Dy–N angle of 139.24(15)°displayed magnetic hysteresis with a coercive field(H_(c))of 18.6 kOe at 2 K,which kept opening up to 35 K.Alternating current susceptibility measurement showed that the relaxation energy barrier reached as high as 1578 K,which is among the highest reported Dy^(Ⅲ)SMMs.Ab initio calculations revealed strong anisotropy and crystal-field axiality of the compound,despite the low symmetry,and provided a synthetically workable approach to construct high-performance SMMs useful in applications such as digital processing,transport electronics,quantumcomputing,and ultra-high-density data storage.

Low-coordination environment design of single Co atoms for efficient CO_(2) photoreduction

Photocatalytic carbon dioxide(CO_(2))to carbon monoxide(CO)offers a promising way for both alleviating the greenhouse effect and meeting the industrial demand.Herein,we constructed a Co single-atom catalyst with intentional low-coordination environment design on porous ZnO(denoted as Co1/ZnO).Impressively,Co1/ZnO exhibited a remarkable activity with a CO yield rate of 22.25 mmol·g^(-1)·h^(-1) and a selectivity of 80.2%for CO_(2) photoreduction reactions under visible light.The incorporation of single Co atoms provided an additional photo-generated electron transfer channel,which suppressed the carrier recombination of photocatalysts.Moreover,the unsaturated Co active sites were capable to adsorb CO_(2) molecule spontaneously,thus facilitating the activation of CO_(2) molecule during CO_(2) reduction course.

Vacancy engineering induced reaction kinetics enhancement of cobalt metaphosphate for pH-universal hydrogen evolution

Developing efficient pH-universal hydrogen evolution reaction(HER)catalysts is critical in the field of water electrolysis,however,which is severely hampered by the sluggish kinetics in alkaline media.Herein,a ruthenium(Ru)incorporation induced vacancy engineering strategy is firstly proposed to precisely construct oxygen vacancy(V_(O))-riched cobalt-ruthenium metaphosphate(CRPO)for high-efficiency pH-universal HER.The V_(O) modifies the electronic structure,improves the superficial hydrophilic and gas spillover capacity,it also reduces the coordination number of Ru atoms and regulates the coordination environment.Theoretical calculations indicate that Ru tends to adsorb H_(2)O and H^(*),whereas V_(O) tends to adsorb OH^(-),which greatly promotes the H_(2)O adsorption and the dissociation of HO-H bond.Ultimately,CRPO-2 exhibits remarkable HER performance,the mass activity is about 18.34,21.73,and 38.07 times higher than that of Pt/C in acidic,neutral,and alkaline media,respectively,at the same time maintain excellent stability.Our findings may pave a new avenue for the rational design of electrocatalysts toward pH-universal water electrolysis.

Low-coordination water Prussian white as cathode for high-performance potassium-ion batteries

Prussian whites(PWs) with a three-dimensional framework can accommodate the insertion and extraction of ions with large radius,which have been widely used in potassium ion batteries.However,PWs show the poor cycling performance and inferior rate ability because of high coordinated water.In this work,PWs with different water content were synthesized via a coprecipitation method by controlling the reaction temperature.The sample with low-coordination water prohibits the best electrochemical performance.It shows a high capacity of 120.5 mAh/g at 100 mA/g for potassium-ion batteries(KIBs).It also exhibits a good rate performance,displaying a capacity of 73.2 mAh/g at 500 mA/g.