Bifunctional Electrocatalysts (Co₉S₈@NSC) Derived from a Polymer‐metal Complex for the Oxygen Reduction and Oxygen Evolution Reactions

Abstract

Bifunctional catalysts for water electrolysis are important for renewable and clean energy transformation processes like fuel cells, lithium−oxygen batteries, and so forth. Despite tremendous efforts, developing efficient bifunctional electrocatalysts with low cost and long‐term durability remains a great challenge. Herein, the synthesis of Co9S8 nanocrystals encapsulated in nitrogen/sulfur‐doped mesoporous graphitized carbon derived from a polymer−metal complex is reported, which exhibit similar electrocatalytic activity and superior stability for water‐splitting reactions (oxygen reduction/oxygen evolution). The remarkable electrochemical properties are mainly attributed to the synergetic effects between Co9S8, heteroatoms and graphitized carbon in alkaline medium, especially for the oxygen evolution reaction. The present strategy to fabricate Co9S8 nanocrystals in nitrogen and sulfur doped carbon using a single‐source precursor offers many prospects in developing highly effective electrocatalysts in rechargeable metal−air batteries.

Cobalt‐Embedded N‐Doped Carbon Arrays Derived In Situ as Trifunctional Catalyst Toward Hydrogen and Oxygen Evolution, and Oxygen Reduction

“…Figure b shows the Raman spectra of Co/MMCs and Co/CNWs. The G‐band located at 1586 cm −1 corresponds to the E 2g mode vibration of graphitic carbon, whereas the D‐band at 1347 cm −1 is associated with the defect mode . The ratio of I D /I G of Co/MMCs is 1.06, whereas which is 1.00 for Co/CNWs.…”

“…The G-band located at 1586 cm À 1 corresponds to the E 2g mode vibration of graphitic carbon, whereas the D-band at 1347 cm À 1 is associated with the defect mode. [40][41][42][43] The ratio of I D /I G of Co/ MMCs is 1.06, whereas which is 1.00 for Co/CNWs. As demonstrated in energy-dispersive X-ray spectroscopy (EDS) images ( Figure S4), the N element content is 5.44 % for Co/ MMCs, higher than that (5.00 %) of Co/CNWs.…”

Graphene‐Encapsulated Co9S8 Nanoparticles on N,S‐Codoped Carbon Nanotubes: An Efficient Bifunctional Oxygen Electrocatalyst

“…The SO x 2À species is considered to be catalytically inactive for the ORR/OER. [7a] The high-resolution N1ss pectrum (Figure 4d), whichc an be deconvoluted into five species,i ncludingp yridinic N (397.67 eV,2 0.1 %), pyrrolic N( 398.20, 7.3 %), graphitic/quaternary N( 401.23, 21.2 %), and N-oxideso fp yridinic N( 403.32 eV, 41.6 %) and CoÀN x (399.02eV, 9.7 %), [17,34] demonstrates that N and Co atoms are indeed embedded in the carbon matrix, and some Co atoms are coordinatedw ith the doped N. It is widely accepted that pyridinic and graphitic N, as well as doped Sand CoÀN x ,a re important catalytically active sites for the ORR/OER. [35] The total contentofp yridinic N, graphitic N, and CoÀN x among all doped Ns pecies reaches up to 70 %, and the content of CÀSÀC and CoÀSa mountst o7 5% of total S. This suggest superior catalytic performance of Co/S/N-800 as electrocatalyst for the ORR/OER.…”

“…[15] These two hybridse xhibitedb etter OER catalytic performance thant he commercial RuO 2 electrocatalyst. [17] Hu et al synthesized Co 9 S 8 /N,S-codoped double-layered carbont ubes by coordination-assisted polymerization and sacrificial-template methods. This hybrid material showede xcellent ORR performance with ah igh half-wave potentialo f0 .83 V, which is comparable to that of the Pt/C electrocatalyst.…”

“…This hybrid material showede xcellent ORR performance with ah igh half-wave potentialo f0 .83 V, which is comparable to that of the Pt/C electrocatalyst. [ [17] Hu et al synthesized Co 9 S 8 /N,S-codoped double-layered carbont ubes by coordination-assisted polymerization and sacrificial-template methods. [18] All these nanohybrids have shown excellent electrocatalytic performances toward both OER and ORR, comparable to those of commercial Pt/C and IrO 2 catalysts.…”