Single-atom catalysts for CO oxidation,CO_(2) reduction,and O_(2) electrochemistry

CO_(x)(x=1,2)and O_(2) chemistry play key roles in tackling global severe environmental challenges and energy issues.To date,the efficient selective electrocatalytic transformations of COx-carbon chemicals,and O_(2)-hydrogenated products are still huge challenges.Single-atom catalysts(SACs)as atomic-scale novel catalysts in which only isolated metal atoms are dispersed on supports shed new insights in overcome these obstacles in CO_(x) and O_(2) chemistry,including CO oxidation,CO_(2) reduction reaction(CO_(2)RR),oxygen reduction reaction(ORR),and oxygen evolution reaction(OER).In this review,the unique features and advanced synthesis strategies of SACs from a viewpoint of fundamental synthesis design are first highlighted to guide future strategy design for controllable SAC synthesis.Then,the to-date reported CO_(2)RR,CO oxidation,OER,and ORR mechanism are included and summarized.More importantly,the design principles and design strategies of improving the intrinsic activity,selectivity,and stability are extensively discussed and the engineering strategy is classified as neighbor coordination engineering,metal-atom engineering,and substrate engineering.Via the comprehensive review and summary of state-of-the-art SACs,the synthesis–structure–property–mechanism–design principle relation can be revealed to shed lights into the structural construction of SACs.Finally,we present an outlook on current challenges and future directions for SACs in CO_(x) and O_(2) chemistry.

Activating lattice oxygen of two-dimensional MnXn-1O2 MXenes via zero-dimensional graphene quantum dots for water oxidation

The poor oxygen evolution reaction(OER)activity of two-dimensional(2 D)transition metal carbides(MXenes)is a major obstacle to their application in highperformance water splitting and fuel cells due to the high energy barriers for the absorption of intermediates.Here,we demonstrate that the lattice oxygen of M_(n)X_(n-1)O_(2)MXenes can be activated by 0 D graphene quantum dots(GQDs),thereby activating the OER via the lattice-oxygen oxidation mechanism(LOM)instead of the conventional adsorbate evolving mechanism.The pH-dependent OER activity of M_(n)X_(n-1)O_(2)@GQDs and ^(18)O isotope-labelling experiments with time-of-flight secondary-ion mass spectrometry(TOF-SIMS)provide the direct evidence of LOM.Interestingly,the activated lattice oxygen amount can be controlled by the GQDs.The as-prepared 0 D/2 D Ti_(3)C_(2)O_(2)@GQDs heterostructure delivers a highly reduced overpotential of 390 mV(bare Ti_(3)C_(2)O_(2):530 mV)at a benchmark current density of 10 mA cm^(-2).Through optimizing the thickness and the additional conductive substrate,the overpotential at 10 mA cm^(-2)decreases to 250 mV,while the Tafel slope is reduced to 39 mV dec^(-1);these values indicate the as-prepared heterostructure is superior to the state-of-the-art MXene-based OER catalysts.This work provides a new strategy to enhance the OER activity of M_(n)X_(n-1)O_(2)and extends the application of LOM from perovskite to MXenes.