Decrypting the Influence of Axial Coordination on the Electronic Microenvironment of Co-N_(5)Site for Enhanced Electrocatalytic Reaction

Metal porphyrins are star molecules that possess welldefined coordination metal centers for versatile catalytic reactions.However,most previous work has focused on the correlations between in-plane symmetric configuration of metal-N_(4)sites and their catalytic performance.Addressing the catalytic contribution of additional axial coordination to such symmetric configuration remains a challenge.Theoretical calculations revealed that axially anchoring an extra pyridine on the tetra-coordinated cobalt porphyrin(Co-N4)to construct penta-coordinated cobalt porphyrin(Co-N_(5))renders cobalt a higher electron density,thereby favoring the rate-determining O_(2)adsorption/activation and reducing the oxygen electroreduction barrier.Therefore,a well-defined Co-N_(5)site is rationally introduced into the azo-linked polymer framework for a fundamental structure-catalytic performance correlation study.As-prepared Co-N_(5)catalyst exhibits a 26 mV positive shift in half-wave potential compared with the pyridine-free Co-N_(4)counterpart,discloses a markedly higher power density(141.4 mW cm^(−2)),and possesses better long-term durability(over 160 h cycles)in a Zn-air battery.Moreover,such a Co-N_(5)catalyst also showcases potential applications for CO_(2)reduction with high CO_(2)-to-CO conversion faradic efficiency and better selectivity than the Co-N_(4)counterpart because coordination of the fifth pyridine evokes electronic localization that suppresses a competitive side reaction.This work proves the positive electrocatalytic contribution of axial penta-coordination on well-defined metalporphyrin-based catalysts and offers atomic understanding of the structure-performance correlation on single atom catalysts for future catalyst design.

Intermetallic PdCd Core Promoting CO Tolerance of Pd Shell for Electrocatalytic Formic Acid Oxidation

Liquid fed fuel cells such as direct formic acid fuel cells(DFAFCs)are considered to be promising power sources for portable electronic devices.However,the poison of CO intermediates on the state-of-the-art platinum and palladium-based electrocatalysts for the formic acid oxidation reaction(FAOR)at the anode hampers the implementation of DFAFCs technologies.Here,we report a core/shell catalyst consisting of intermetallic PdCd core and Pd shell(i-PdCd@Pd)with promoted CO anti-poison ability and thus FAOR performance.The optimal i-PdCd@Pd catalyst exhibits a high mass activity and specific activity at peak potential,which are 24 and 4 times greater than that of commercial Pd/C catalyst,respectively.We understand by in-situ surface-enhanced infrared absorption spectroscopy(ATR-SEIRA)and X-ray photoelectron spectroscopy(XPS)that in i-PdCd@Pd,the intermetallic PdCd under-layers can induce the downshift of d-band center of surface Pd atoms,which would improve the CO tolerance and thus promote the FAOR performance.