Cobalt Amide Imidate Imidazolate Frameworks as Highly Active Oxygen Evolution Model Materials

Abstract

Two imidazolate-based Co-MOFs, IFP-5 and IFP-8 (imidazolate framework Potsdam), with a different peripheral group −R (−Me and −OMe, respectively) have been synthesized by a solvothermal method and tested toward the oxygen evolution reaction (OER). Remarkably, IFP-8 presents much lower overpotentials (319 mV at 10 mA/cm2 and 490 mV at 500 mA/cm2) than IFP-5 toward OER, as confirmed by online gas chromatography measurements (Faradaic yield of O2 > 99%). Moreover, the system is extraordinarily stable during 120 h, even when used as a catalyst toward the overall water splitting reaction without any sign of fatigue. An integrated ex situ spectroscopic study, based on powder X-ray diffraction, extended X-ray absorption fine structure, and attenuated total reflection, allows the identification of the active species and the factors that determine the catalytic activity. Indeed, it was found that the performances are highly affected by the nature of the −R group, because this small change strongly influences the conversion of the initial metal organic framework to the active species. As a consequence, the remarkable activity of IFP-8 can be ascribed to the formation of Co(O)OH phase with a particle size of a few nanometers (3–10 nm) during the electrocatalytic oxygen evolution.

A Molecular Tetrahedral Cobalt–Seleno-Based Complex as an Efficient Electrocatalyst for Water Splitting

“…However, since not each and every metal atom is expected to be involved in the reaction, the actual TOF could be evidently underestimated. However, the calculated TOF for CoSe4@Au-glass is still important (Table 1), and is comparable or higher than that of other cobalt-based catalysts previously reported under similar conditions [50,51]. The stability of the CoSe4@Au-glass electrode under long-term electrolysis in alkaline medium was also investigated using the chronoamperometric technique by which the current density was measured at a constant applied potential of 1.53 V vs. RHE for prolonged period of time, as shown in Figure 3c.…”

Rational Design of a N,S Co‐Doped Supermicroporous CoFe–Organic Framework Platform for Water Oxidation

“…As a result, its catalytic performance continuously decreased (Figure S10). As a consequence, compared with the pristine SyA‐Co 2 Fe, the high OER performance for this N,S co‐doped MOF, SyA‐Co 2 Fe‐ST, should mainly be ascribed to higher electrochemical activation toward the active species via in situ surface modification during OER process . Thus, combining the above characterization and results.…”

“…However, there is rarely a report about doping heteroatoms into direct MOF materials for electrocatalytic water splitting. Furthermore, very recently, the experimental results have shown that the substituent groups of organic ligands in MOFs could highly influence the performances because the different substituent groups could strongly affect the conversion of the initial MOF to the active species …”

“…Metal–organic frameworks (MOFs), especially, pillared‐layered MOFs, are rising star materials in the field of materials science because of their ultrafine porosity, rich active metal‐sites and tunable structures, which have attracted enormous interest and have a widespread application in catalysis, energy conversion technologies, and environmentally friendly technologies . In particular, MOFs have been employed as high active electrocatalysts to improve the sluggish reaction kinetics of water oxidation [i.e., the oxygen evolution reaction (OER)] as one of the determine steps and the key processes in water splitting and metal–air batteries . However, most of direct MOFs as electrocatalysts have poor long‐term electrochemical durability in reaction media (strong acid or strong base), limiting their practical application in the field of water splitting since the long‐term stability and high activity are equally important for catalysts .…”

Recent progress in pristine MOF-based catalysts for electrochemical hydrogen evolution, oxygen evolution and oxygen reduction

“…To understand how to control the transformation of the MOF to the active catalytic phase, Bucci and coworkers used two MOF models that only differ in the substituent at the imidazole C2 position of the ligand (IFP-5 with a -Me; IFP-8 with an -OMe). 148 At pH 14, IFP-8 presented much lower overpotentials (319 mV) than IFP-5 (340 mV) at 10 mA cm −2 toward the OER and was found with structure conversion and formation of the Co(O)OH phase (3-10 nm particles) after the OER process. As indicated by the further integrated ex situ spectroscopic study, the -R group could affect greatly the hydrolysis rate of the initial MOF framework in an alkaline environment, which would influence the formation of the Co(O)OH active phase that associated with the final electrochemical activity.…”