Metathesis Reaction to Form Nanosheet-Structured Co(OH)₂ Deposited on N-Doped Carbon as Composite Electrocatalysts for Oxygen Reduction

Abstract

Developing effective non-precious metal electrocatalysts for oxygen reduction reaction (ORR) with a simple synthesis procedure is of great importance in a wide range of clean energy conversion systems. In this work, several ORR composite electrocatalysts with Co­(OH)2 nanosheets deposited on N-doped carbon (Co­(OH)2/NC) are comparatively synthesized at room temperature by simple and cost-effective methods using sodium borohydride (NaBH4), ethylene glycol (C2H6O2), and hydrazine hydrate (N2H4) as the reducing agents as well as the metathesis reaction of directly reacting with KOH without a reducing agent. As a result, the Co­(OH)2/NC prepared by directly using KOH (Co­(OH)2/NC-KOH) displays a higher electrocatalytic activity, methanol tolerance, and stability than the other three. Results of X-ray diffraction (XRD), Raman, transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) demonstrate that Co­(OH)2/NC-KOH has a structure of N-doped carbon-supported β-Co­(OH)2 with a Brunauer–Emmett–Teller (BET) surface area of 872 m2/g. This electrocatalytic activity of Co­(OH)2/NC comes from a strong synergistic electrocatalysis from N-doped carbon and Co­(OH)2 nanosheets. For fundamental understanding, a synergistic ORR electrocatalysis mechanism on Co­(OH)2/NC is also proposed in this paper.

Hierarchical FeO(OH)–CoCeV (Oxy)hydroxide as a Water Cleavage Promoter

“…These redox peaks P 3 and P 4 resulted from the reduction of Co­(IV) to Co­(III) and Co­(III) to Co­(II), respectively. , In the composite FeO­(OH)–CoCeV-LTH, the onset oxidation potential of Co 3+ /Co 4+ (1.41 V) is more negative as compared to CoCeV-LTH (1.43 V), signifying that Co 3+ oxidation is more favorable on the composite. From the reported literature, the higher oxidation states of Fe 3+ and Co 3+ species are known to contribute to an enhancement in the HER and OER activity, which explains the higher activity of FeO­(OH)–CoCeV-LTH toward the overall water splitting. − Figure C represents the proposed redox reaction mechanism involved in FeO­(OH) and CoCeV-LTH. In step (1), FeO­(OH) by virtue of its water cleavage promoting OH attached to the metal center, which helps to keep the core metal center at its highest oxidation state, promotes the electron acceptor capability of Fe 3+ and can get easily reduced to Fe 2+ (Fe­(OH) 2 ) generating OH – .…”

Transition Metal (Fe, Ni, Mn) with Heteroatoms B and S Tri-doped Co/C Catalysts for Oxygen Reduction Reaction

“…As illustrated in Figure , MBS-Co/C (M = Fe, Ni, Mn) catalysts are successfully synthesized via a metathesis reaction followed by a one-step pyrolysis process. First, a Co­(OH) 2 /C composite is prepared from reacting CoCl 2 with KOH on carbon (high specific surface area) . MBS-Co/C catalysts are then obtained through pyrolyzing the mixed precursors of Co­(OH) 2 /C, M salt, H 3 BO 3 , and S at an equivalent amount, where M = Fe, Ni, and Mn.…”

“…In this work, Co­(OH) 2 /C was synthesized by reacting CoCl 2 with KOH, where carbon (1.0 g) and cobalt chloride (0.4482 g) were dispersed and dissolved completely in 20 mL of deionized water, and then 10 mL of a 1 M KOH solution was dropped, followed by ultrasonic treatment for 30 min. , The formed precipitate was filtered and dried.…”

“…This relatively open structure has accessible catalytic active sites to improve high catalytic activity. Recently, we used a metathesis reaction to prepare Co­(OH) 2 /C, namely, Co­(OH) 2 nanosheets supported on C, and applied as the catalyst for ORR . However, enhancing the catalyst’s performance for ORR still remains challenging.…”

“…On the other hand, heteroatom-doped carbon is a type of a metal-free catalyst for ORR based on the difference of electronegativity between heteroatoms and C, which polarizes the carbon matrix efficiently and facilitates the adsorption of O 2 , thus benefiting the catalysis of ORR. ,, Furthermore, heteroatom dual-doped carbon materials have been extensively studied because of the synergistic catalysis effect of different heteroatoms. − Although heteroatom-doped carbon catalysts have obtained much attention, their ORR catalytic performances are not good enough compared with Pt/C. , In this way, preparing composite catalysts, namely, heteroatom-doped carbon combined with metal-based materials has become necessary . In addition, C. Zhu and his co-workers recently reported atomically dispersed Fe sites on N-doped carbon by a secondary-atom-doped strategy to improve the number and reactivity of the active site and enlarge the surface area simultaneously .…”