Significance Seawater is one of the most abundant resources on Earth. Direct electrolysis of seawater is a transformative technology for sustainable hydrogen production without causing freshwater scarcity. However, this technology is severely impeded by a lack of robust and active oxygen evolution reaction (OER) electrocatalysts. Here, we report a highly efficient OER electrocatalyst composed of multimetallic layered double hydroxides, which affords superior catalytic performance and long-term durability for high-performance seawater electrolysis. To the best of our knowledge, this catalyst is among the most active for OER and it advances the development of seawater electrolysis technology.

High-performance seawater oxidation by a homogeneous multimetallic layered double hydroxide electrocatalyst

The oxygen evolution reaction (OER) is crucial to electrochemical hydrogen production. However, designing and fabricating efficient electrocatalysts still remains challenging. By confinedly coordinating organic ligands with metal species in layered double hydroxides (LDHs), an innovative LDHs-assisted approach is developed to facilely synthesize freestanding bimetallic 2D metal-organic framework nanosheets (2D MOF NSs), preserving the metallic components and activities in OER. Furthermore, the research has demonstrated that the incorporation of carboxyl organic ligands coordinated with metal atoms as proton transfer mediators endow 2D MOF NSs with efficient proton transfer during the electrochemical OHads  → Oads transition. These freestanding NiFe-2D MOF NSs require a small overpotential of 260 mV for a current density of 10 mA cm-2 . When this strategy is applied to LDH nanosheets grown on nickel foam, the overpotential can be reduced to 221 mV. This outstanding OER activity supports the capability of multimetallic organic frameworks for the rational design of water oxidation electrocatalysts. This strategy provides a universal path to the synthesis of 2D MOF NSs that can be used as electrocatalysts directly.

Freestanding 2D NiFe Metal-Organic Framework Nanosheets: Facilitating Proton Transfer via Organic Ligands for Efficient Oxygen Evolution Reaction.

Harmful and toxic gas sensing techniques are of vital importance for ecological environment. Abundant physical and chemical properties of metal-organic frameworks (MOFs) have been discovered gradually, such as luminescence, catalysis, and electrical conductivity, which make MOFs evolve into a kind of powerful sensing materials. Although many reported MOF-based sensors have been well reviewed, a comprehensive summary focused on the extremely toxic and harmful gas/vapor sensors is missing. In this review, from a different perspective, the major advances and applications of MOF-based sensors towards the very harmful and toxic analytes in the gas or vapor phase are reviewed, and the sensing mechanisms are also highlighted in detail. Finally, the critical challenges and prospects in this field are discussed from a macro point of view. It is expected that this review could offer a guidance of current state-of-art state on MOF-based hazardous gas/vapor sensors, and accelerates the further practical applications. 

Advances in metal-organic frameworks-based gas sensors for hazardous substances

Metal-organic frameworks (MOFs) are considered potential electrocatalysts for efficient water splitting. However, the structure-activity relationship of most MOFs is not systematically analyzed for electrocatalysis for anodes and cathodes. In this paper, we provide a strategy to modulate the electronic microstructure of iron-based bimetallic MOFs (MFe-BDC (M: Mg, Zn, Cd)) grown on the nickel foam (NF) as bifunctional electrocatalysts for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). The optimal bimetallic CdFe-BDC via modulating appropriate metal cations of IIA and IIB possesses excellent OER and HER performance with the lowest overpotentials of 290 mV at 100 mA cm-2 and 148 mV at 10 mA cm-2, respectively. The overall water splitting performance of the as-prepared CdFe-BDC requires 1.68 V to achieve a current density of 10 mA cm-2 in the real seawater media, and it exhibits the competitive H2 and O2 production rates of 6.4 and 3.1 μL s-1, respectively, in ambient alkaline conditions, suggesting its potential practical applications. Density functional theory (DFT) calculations demonstrate the relationship between microstructure and electrocatalytic performance of bimetallic MFe-BDC. This work emphasizes the significance of tailoring the electronic microstructure of bimetallic MOFs for efficient overall water splitting in alkaline and seawater environment.

Structural and Electronic Modulation of Iron-Based Bimetallic Metal-Organic Framework Bifunctional Electrocatalysts for Efficient Overall Water Splitting in Alkaline and Seawater Environment.

Lithium-oxygen batteries (LOBs) have presented great promise in next-generation energy storage systems due to their high theoretical energy density. However, the sluggish deposition and decomposition kinetics of lithium peroxide (Li2O2)...

Accelerating Reaction Kinetics of Lithium-Oxygen Chemistry by Modulating Electron Acceptance-Donation Interaction in Electrocatalysts

Co-based bimetallic metal-organic frameworks (MOFs) have emerged as a kind of promising electrocatalyst for oxygen evolution reaction (OER). However, most of present works for Co-based bimetallic MOFs are still in try-and-wrong stage, while the OER performance trend and the underlying structure-function relationship remain unclear. To address this challenge, Co-based MOFs on carbon cloth (CC) (CoM MOFs/CC, M = Zn, Ni, and Cu) are prepared through a room-temperature method, and their structure and OER performance are compared systematically. Based on the results of overpotential and Tafel slope, the order of OER activity is ordered in the decreasing sequence: CoZn MOF > CoNi MOF > CoCu MOF > Co MOF. Spectroscopic studies clearly show that the better OER performance of CoM MOFs results from the higher oxidation state of Co, which is related to the choice of second metal. Theoretical calculations indicate that CoZn MOFs possess strengthened adsorption for O-containing intermediate, and lower energy barrier towards OER. This study figures out the effect of second metal on the OER performance of Co-based bimetallic MOFs and suggests that tuning the electronic structure of the metal site can be an effective strategy for other MOFs-based OER catalysts.

Jianying Zhao

Papers

Understanding the Effect of Second Metal on CoM (M = Ni, Cu, Zn) Metal-Organic Frameworks for Electrocatalytic Oxygen Evolution Reaction.