Carbon-supported Co(III) dimer for oxygen reduction reaction in alkaline medium

Abstract

Non-precious metal electrocatalysts obtained by pyrolysis of precursors of metal, nitrogen, and carbon (MNC) are viewed as an inexpensive replacement for platinum-based electrocatalysts for the oxygen reduction reaction (ORR) in fuel cells. The hypothesized ORR active site structure of typical MNC catalysts consists of a transition metal coordinated to the pyridinic/pyrollic type of nitrogen covalently attached to the edges of the graphitic crystallites. One of the drawbacks of all the reported procedures to synthesize these MNC electrocatalysts is the inability to control the formation of a specific active site structure suitable for ORR. Lack of clarity on the active site structure limits the researcher's ability to design a synthesis methodology that maximizes the specific active site density. In this study, we have synthesized a Co(III) dimer ([Co 2 (OH) 2 (OOCCH 3 ) 3 (bpy) 2 ] NO 3 ⋅ 1.5 H 2 O) and demonstrated its ORR activity in alkaline medium. The ORR activity and methanol tolerance property of the Co(III) dimer were compared with those of Ketjenblack carbon (used as support for Co(III) dimer) and commercial 20 wt% Pt/C, respectively. Since Co(III) dimer is a molecular material, its characterization by single-crystal X-ray diffraction, nuclear magnetic resonance, and infrared studies revealed the chemical structure unambiguously. Density functional theory calculation predicted the possibility of both end-on and side-on oxygen adsorption at the metal center of the Co(III) dimer.

Nickel-Based Hybrid Material for Electrochemical Oxygen Redox Reactions in an Alkaline Medium

“…The percentage of HO 2 – production and n value were estimated at around 41% and 3.3 over the potential range of 0.75–0.40 V versus RHE, respectively. The available Ni 2+/3+ active sites (64.92 × 10) for oxygen redox reactions were calculated via the charge associated with Ni 3+/2+ reduction peak. Four- and two-electron TOFs of ORR on Ni-BTB-BPE/C catalyst were calculated to be 2.24 and 0.84 electrons [Ni] −1 s –1 at 0.70 V versus RHE, respectively.…”

“…Recently, metal–organic frameworks (MOFs), ,− coordination polymers (CPs), and metal–organic complexes (MOCs) − have been reported as promising electrocatalysts for ORR and/or OER, owing to their hierarchy of architectures, tunable chemical structure, large surface area, high porosity and isolated active sites . However, there are relatively fewer materials reported as electrocatalysts for oxygen redox reactions. − Low intrinsic electrical conductivity and weak structural integrity in strong alkaline conditions hampered their applications in energy conversion systems.…”

“…However, there are relatively fewer materials reported as electrocatalysts for oxygen redox reactions. − Low intrinsic electrical conductivity and weak structural integrity in strong alkaline conditions hampered their applications in energy conversion systems. Synthesis of conductive MOFs/CPs supported on high surface area carbons − or pyrolysis − are few frequently adopted techniques to improve the electron transfer and the mass utility of MOFs/CPs. Miner et al have synthesized an electrically conductive (σ = 40 S cm –1 ) two-dimensional layered structure with M–N 4 units, which shows a two- and four-electron turn-over frequencies (TOFs) of 0.014 and 0.017 electrons [Ni] −1 s –1 for oxygen reduction, respectively .…”

“…However, thermal treatment destroys the 3D network of MOF and produces several unoptimized active sites for ORR/OER. One strategy that has been adapted to improve the electron transport without disrupting the semiconductive MOF/CP structure is to adsorb them on high surface area carbons such as Ketjenblack EC-600JD, , graphene, − and carbon nanotubes. , …”

Improved Oxygen Redox Activity by High-Valent Fe and Co3+ Sites in the Perovskite LaNi1–xFe0.5xCo0.5xO3

“…As a result, they are prohibitively expensive and scarcely employed in large-scale production . To end this, redox-active transition metal-based nonprecious metal catalysts (perovskites, 2D-layers, metal–nitrogen–carbons, metal-complexes, metal–organic frameworks, and coordination polymers) are emerging as potential alternative catalysts for oxygen redox reactions. − …”