Use of Cobalt Polyphthalocyanine and Graphene as Precursors to Construct an Efficient Co₉S₈/N,S‐G Electrocatalyst for the Oxygen Electrode Reaction in Harsh Media

Abstract

The oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are fundamental reactions connected with energy conversion and/or storage devices. However, the sluggish kinetics of the ORR and OER reduce the efficiency. To address these issues, the development of efficient and robust electrode catalysts is required desperately. Herein, a new Co9S8 nanocrystal hybrid anchored on a N‐ and S‐dual‐doped graphene (Co9S8/N,S‐G) was prepared by a two‐step method, namely, a π–π assembly process of p‐phenyl‐bis(3,4‐dicyanophenyl)thioether cobalt polyphthalocyanine (PTCoPPc) and graphene oxide and a pyrolysis procedure. Electrochemical studies demonstrated that Co9S8(800)/N,S‐G exhibited a comparable ORR performance with 20 wt % Pt/C, such as an onset potential and a half‐wave potential of 0.931 and 0.811 V vs. the reversible hydrogen electrode, respectively, a limiting current density of 5.207 mA cm−2, and a good long‐term stability with a current retention of 92.6 % after 10 000 s continuous measurements. Co9S8(900)/N,S‐G displayed an excellent OER activity, which was ascribed to the presence of pyridinic N, graphitic N, and the occupation of Co−N to catalyze the ORR; and the oxygen adsorption on the surface of Co9S8(900)/N,S‐G contributed significantly to the OER activity. The approach developed here offered a new strategy to construct efficient oxygen electrode catalysts.

Generalized Synthesis of Ultrathin Cobalt‐Based Nanosheets from Metallophthalocyanine‐Modulated Self‐Assemblies for Complementary Water Electrolysis

“…The structure of CoPc/rGO assembly was characterized by X‐ray diffraction (XRD) and Raman spectrum. Appearance of XRD peaks assigned to CoPc and Raman signals attributed to A 1g and B 1g vibration modes for CoPc (Figure S1, Supporting Information) confirms the successful assembly between CoPc and rGO via π–π interaction (as shown in Figure A,B) . Moreover, owing to the introduction of rGO, the Raman speaks of CoPc/rGO assembly around 1370 and 1595 cm −1 broaden compared to that of pure CoPc.…”

“…Giving that the similar planar structure and electronic features, it would be prone to face‐to‐face assemble with graphene by π–π interaction to form 2D structure. Meanwhile, the external ring derived from tetrapyrrole may also work as ligand‐capped agents to confine the undesirable aggregation, and even bind growth of nanoparticles during the subsequent heat treatment . Therefore, small‐sized nanoparticles would connect with each other to form NSs.…”

Facile and Controllable One‐Pot Synthesis of Hierarchical Co9S8 Hollow Microspheres as High‐Performance Electroactive Materials for Energy Storage and Conversion

“…It is noted that Co 9 S 8 @C‐2 shows a smaller Tafel slope of 66 mV dec −1 than Co 9 S 8 @C‐10 (85 mV dec −1 ) and Co 9 S 8 @C‐20 (159 mV dec −1 ), which indicates the former exhibits the highest OER activity among the composite electrocatalysts. Furthermore, Tafel slope of Co 9 S 8 @C‐2 is smaller compared with those of other Co 9 S 8 based electrocatalysts including Co 9 S 8 @SNCC (80 mV dec −1 ), N‐Co 9 S 8 /G (82.7 mV dec −1 ), Co 9 S 8 HMs‐140/C (113 mV dec −1 ), Co 9 S 8 @CoS@CoO@C NPs (81 mV dec −1 ), Co 9 S 8 @NOSC‐900 (68 mV dec −1 ), and Co 9 S 8 (900)/N, S−G (73 mV dec −1 ) . To further verify the aforementioned results, the EIS measurements on Co 9 S 8 @C were performed at η=0.47 V from 10 5 to 0.01 Hz with an AC voltage of 5 mV.…”

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.…”

“…LSV curves (Figure 6a) reveal that Co/S/N-800 has ac omparable OER onset potential ( % 1.56 V) and higher anodic current density than commercial RuO 2 (1.57 V).A lthough the OER onsetp otential of Co/S/N-800 is slightly higher than that of 20 wt %Ir/C (1.52 V), its OER catalytic current largely exceeds that of Ir/C at appliedp otentials above 1.63 V. In addition, ac learo xidation peak attributed to the conversion Co 2 + !Co 3 + !Co 4 + is observed in the potential range of 1.30-1.50 V. The formation of more cobalti ons in higher valance states on the Co 9 S 8 surface before the OER process is widely believed to be beneficial for the OER. [34] Generally,t he potentiala tac urrent density of 10 mA cm À2 is one of the key parameters to evaluate the electrocatalytic activity for the OER. Co/S/N-800r eaches ap otential of 1.591 Vatacurrent density of 10 mA cm À2 ,w hich is much lower than that of commercial RuO 2 ,c omparable to that of 20 wt %I r/C (1.557 V), and suggestsh ighly efficient OER performance.…”