Bimetallic metal–organic frameworks and MOF-derived composites: Recent progress on electro- and photoelectrocatalytic applications

Oxygen evolution reaction (OER), as a relevant half reaction for water splitting to address the energy crisis, has captured a great deal of attention. However, this technology has always been impeded by the lack of a highly efficient and stable electrocatalyst. Amorphous materials, which possess long‐range disorder and only short‐range order over a few atoms, are often superior to their crystalline counterparts in electrocatalysis owing to their more active sites, broader chemical composition range, and more structural flexibility. This review first introduces some assessment criteria for the OER and then presents theoretical modeling of the OER mechanisms and the state‐of‐the‐art amorphous transition metal‐based OER electrocatalysts, involving oxides, hydroxides, sulfides, phosphides, borides, and their composites, as well as their practical applications in the OER. Finally, recent development, existing challenges, and future perspectives for amorphous transition metal‐based OER electrocatalysts are discussed. This paper offers valuable guidance in designing highly efficient and stable amorphous OER electrocatalysts for future energy applications.

Recent Development and Future Perspectives of Amorphous Transition Metal‐Based Electrocatalysts for Oxygen Evolution Reaction

It is highly desirable to cut down the electron transfer resistance, improve both site activity and site populations of layered double hydroxides (LDHs) for enhanced electrochemical activity of oxygen evolution reaction (OER). Herein, the hybrid that Co-LDH nanosheets shells grown on Ag nanowires (NWs) cores (Ag@Co-LDH) was constructed and applied as a favorable OER electrocatalyst. The high conductivity of Ag NWs and heterointerface between Ag NWs and Co-LDH gravely accelerate electron transfer. Co-LDH with ultrathin sheet-like structure and abundant grain boundary defects effectively provide lots of active sites. The optimized local environment of Co atoms by Ag dopants and plentiful amorphous regions strongly enhance the intrinsic activity of active site. Therefore, the as-prepared Ag@Co-LDH demonstrates distinguished OER activity with a low overpotential of 217 mV at the current density of 10 mA cm−2, which is superior to most reported advanced OER electrocatalysts and even commercial Ir/C. Moreover, benefiting from the unique structure and stable heterointerface, Ag@Co-LDH also exhibits robust cycling stability and long-term durability proved by accelerated degradation test (ADT) and galvanostatic test, respectively. This finding provides a practical design direction for high-performance LDH-based OER electrocatalysts.

Hierarchically constructed Ag nanowires shelled with ultrathin Co-LDH nanosheets for advanced oxygen evolution reaction

Electrochemical water splitting is a mature technology for hydrogen generation. Numerous studies have focused on the development of highly efficiency electrocatalysts to produce hydrogen and oxygen from water electrolysis through...

First-row transition metal-based materials derived from bimetallic metal-organic frameworks as highly efficient electrocatalysts for electrochemical water splitting

A self-supporting electrode with in-situ partial transformation of Fe-MOF into amorphous NiFe-LDH for efficient oxygen evolution reaction

Since the complicated multiple electron transfer process and slow kinetics in the OER process seriously hinder the electrochemical decomposition of water, it is urgent to design and develop electrocatalysts with excellent performance and superior stability to reduce overpotential and accelerate the reaction dynamics of the OER. Herein, a unique ultra-thin nanosheet bimetal electrocatalyst NiFe-MOF/IF was synthesized by a one-step hydrothermal method, and characterized by SEM, XRD, TEM, and XPS. NiFe-MOF/IF shows superior OER electrocatalytic activity in 1 M KOH electrolyte solution, and an ultralow overpotential of only 230 and 262 mV was required to achieve a current density of 10 and 100 mA cm-2, respectively, with a relatively small Tafel slope of 30.46 mV dec-1 for the OER. No obvious degradation of the current density at 10 mA cm-2 was observed over about 16 h, which indicates the excellent stability of the catalyst. Favourable activity and benign durability of NiFe-MOF/IF can be attributed to the three-dimensional high porosity conductive substrates, in situ growth of MOF nanosheets, bimetallic synergy, and unique layering. This research provides a promising strategy for the application of MOF materials in the field of electrocatalysis.

In situ assembly of bimetallic MOF composites on IF as efficient electrocatalysts for the oxygen evolution reaction.

A nanoflower composite catalyst in situ grown on conductive iron foam: revealing the enhancement of OER activity by cooperating of amorphous Ni based nanosheets with spinel NiFe2O4

Due to the slow kinetics of oxygen evolution at the anode, the efficiency of electrocatalytic water decomposition is critically reduced, and its large-scale application is severely restricted. Therefore, it is urgent to develop electrocatalysts with excellent performance and stability to accelerate the oxygen evolution reaction (OER) reaction kinetics. Herein, a self-supporting binder-free electrocatalyst was successfully prepared using in situ grown Cu(OH)2 nanowires on CF as the carrier to grow ZIF-67 via a room temperature immersion method. The combination of Cu(OH)2 nanowires and the unique structure of ZIF-67 forms a three-dimensional nanostructured catalyst, in which the unique structure and the existence of synergy may contribute to a larger electrochemical active surface area, expose more electrochemically active sites, adjust the electronic structure, and accelerate the rate of electron transfer, thus greatly improving the electrocatalytic activity and durability for OER. The as-prepared Cu(OH)2@ZIF-67/CF exhibited excellent OER performance under alkaline conditions and required overpotentials of 205 mV and 276 mV to drive current densities of 10 mA cm−2 and 100 mA cm−2, respectively, with a small Tafel slope of 70.5 mV dec−1 for OER. The stability test of Cu(OH)2@ZIF-67/CF at the current density of 10 mA cm−2 displayed excellent stability for 22 h. This study provides a feasible strategy for the rapid preparation of low-cost and efficient electrocatalysts in alkaline media.

Lei Ye

Papers

Hierarchically constructed Ag nanowires shelled with ultrathin Co-LDH nanosheets for advanced oxygen evolution reaction

A self-supporting electrode with in-situ partial transformation of Fe-MOF into amorphous NiFe-LDH for efficient oxygen evolution reaction

In situ assembly of bimetallic MOF composites on IF as efficient electrocatalysts for the oxygen evolution reaction.

A nanoflower composite catalyst in situ grown on conductive iron foam: revealing the enhancement of OER activity by cooperating of amorphous Ni based nanosheets with spinel NiFe2O4

Assembly of ZIF-67 nanoparticles and in situ grown Cu(OH)2 nanowires serves as an effective electrocatalyst for oxygen evolution.