Interfacial Micro-Environment of Electrocatalysis and Its Applications for Organic Electro-Oxidation Reaction

Conventional designing principal of electrocatalyst is focused on the electronic structure tuning, on which effectively promotes the electrocatalysis. However, as a typical kind of electrode-electrolyte interface reaction, the electrocatalysis performance is also closely dependent on the electrocatalyst interfacial micro-environment (IME), including pH, reactant concentration, electric field, surface geometry structure, hydrophilicity/hydrophobicity, etc. Recently, organic electro-oxidation reaction (OEOR), which simultaneously reduces the anodic polarization potential and produces value-added chemicals, has emerged as a competitive alternative to oxygen evolution reaction, and the role IME played in OEOR is receiving great interest. Thus, this article provides a timely review on IME and its applications toward OEOR. In this review, the IME for conventional gas-involving reactions, as a contrast, is first presented, and then the recent progresses of IME toward diverse typical OEOR are summarized; especially, some representative works are thoroughly discussed. Additionally, cutting-edge analytical methods and characterization techniques are introduced to comprehensively understand the role IME played in OEOR. In the last section, perspectives and challenges of IME regulation for OEOR are shared.

Switching the Oxygen Evolution Mechanism on Atomically Dispersed Ru for Enhanced Acidic Reaction Kinetics

Designing stable single-atom electrocatalysts with lower energy barriers is urgent for the acidic oxygen evolution reaction. In particular, the atomic catalysts are highly dependent on the kinetically sluggish acid-base mechanism, limiting the reaction paths of intermediates. Herein, we successfully manipulate the steric localization of Ru single atoms at the Co3O4 surface to improve acidic oxygen evolution by precise control of the anchor sites. The delicate structure design can switch the reaction mechanism from the lattice oxygen mechanism (LOM) to the optimized adsorbate evolution mechanism (AEM). In particular, Ru atoms embedded into cation vacancies reveal an optimized mechanism that activates the proton donor-acceptor function (PDAM), demonstrating a new single-atom catalytic pathway to circumvent the classic scaling relationship. Steric interactions with intermediates at the anchored Ru-O-Co interface played a primary role in optimizing the intermediates' conformation and reducing the energy barrier. As a comparison, Ru atoms confined to the surface sites exhibit a lattice oxygen mechanism for the oxygen evolution process. As a result, the delicate atom control of the spatial position presents a 100-fold increase in mass activity from 36.96 A gRu(ads)-1 to 4012.11 A gRu(anc)-1 at 1.50 V. These findings offer new insights into the precise control of single-atom catalytic behavior.

Modulation of High-Spin Co(II) in Li/Co-MOFs as Efficient Fenton-like Catalysts

Developing high-performance catalysts toward the Fenton reaction is important for environmental protection and sustainable development, yet it is still challenging. The high-spin states of first-row transition metal atoms with tetrahedral coordination provide a flexible electronic environment to activate the catalyst and elevate its catalytic activity. As a type of material with adjustable structures, metal-organic frameworks (MOFs) are excellent candidate catalysts as they can accurately regulate the coordination configurations of metal ions. In this paper, we investigate and summarize the direct formation of bimetallic carboxylate Li/Co-MOFs with tetrahedral coordination metal centers in a mixed H2O/polar organic solvent system. The induction of Li(I) ions is manifested in the generation of hydroxides during the dissociation of the Co(II) solvation structure to trigger the tetrahedral coordination behavior of Co(II). These Li/Co-MOFs containing high-spin Co(II) centers can serve as highly efficient Fenton-like catalysts for organics. This study provides a promising strategy for rational design of MOF-based catalysts with high-spin metal centers for application in environment governance.

Microwave-assisted rapid synthesis and activation of ultrathin trimetal-organic framework nanosheets for efficient electrocatalytic oxygen evolution

Ultrathin metal-organic frameworks (MOFs) nanosheets have been considered as one of promising electrocatalysts for oxygen evolution reaction due to their unique structures. However, the preparation process is subject to the low-yield exfoliation and time-consuming synthetic methods. And it still requires to be explored to develop an efficient strategy for regulation of surface electronic states of MOFs to enhance their electrocatalytic activities. Herein, we report a facile microwave-assisted synthesis of NiCoFe-based trimetallic metal-organic framework (MOF) nanosheets, which can achieve simultaneously rapid synthesis and activation of MOF for OER. The as-prepared Ni₄Co₄Fe₂-MOF nanosheets exhibit excellent OER activity and electrochemical stability, which can deliver a current density of 10 mA cm^-2 at a low overpotential of 243 mV with a small Tafel slope of 48.1 mV dec^-1. This work provides a facile method for the rapid synthesis of MOF nanosheets and also demonstrates an effective approach for regulating the electronic structure of MOFs for electrocatalysis.

Isostructural MOFs with Higher Proton Conductivity for Improved Oxygen Evolution Reaction Performance

Here we synthesized two new isostructural MOFs (FJU-82-Co/FJU-82-Zn) and first observed that tuning of the proton conductivity may provide an effective strategy to improve the electrocatalytic OER perfomances of isostructural crystalline MOF materials. The conductivity value for FJU-82-Co is 7.40 × 10^-5 S cm^-1, which is 127-fold that for FJU-82-Zn with 5.80 × 10^-7 S cm^-1 at 60 °C and 98% RH, while the overpotential of FJU-82-Co is 0.57 V at 1 mA cm^-2, which is better than that of FJU-82-Zn with 1.17 V.