Water electrolysis, a process for producing green hydrogen from renewable energy, plays a crucial role in the transition toward a sustainable energy landscape and the realization of the hydrogen economy. Oxygen evolution reaction (OER) is a critical step in water electrolysis and is often limited by its slow kinetics. Two main mechanisms, namely the adsorbate evolution mechanism (AEM) and lattice oxygen oxidation mechanism (LOM), are commonly considered in the context of OER. However, designing efficient catalysts based on either the AEM or the LOM remains a topic of debate, and there is no consensus on whether activity and stability are directly related to a certain mechanism. Considering the above, we discuss the characteristics, advantages, and disadvantages of AEM and LOM. Additionally, we provide insights on leveraging the LOM to develop highly active and stable OER catalysts in future. For instance, it is essential to accurately differentiate between reversible and irreversible lattice oxygen redox reactions to elucidate the LOM. Furthermore, we discuss strategies for effectively activating lattice oxygen to achieve controllable steady-state exchange between lattice oxygen and an electrolyte (OH− or H2O). Additionally, we discuss the use of in situ characterization techniques and theoretical calculations as promising avenues for further elucidating the LOM.
Electrocarboxylation of carbon dioxide (CO2) using organic substrates has emerged as a promising method for the sustainable synthesis of value-added carboxylic acids due to its renewable energy source and mild reaction conditions. The reactivity and product selectivity of electrocarboxylation are highly dependent on the cathodic behavior, involving a sequence of electron transfers and chemical reactions. Hence, it is necessary to understand the cathodic reaction mechanisms for optimizing reaction performance and product distribution. In this work, a review of recent advancements in the electrocarboxylation of CO2 with organic substrates based on different cathodic reaction pathways is presented to provide a reference for the development of novel methodologies of CO2 electrocarboxylation. Herein, cathodic reactions are particularly classified into two categories based on the initial electron carriers (i.e., CO2 radical anion and substrate radical anion). Furthermore, three cathodic pathways (ENE(N), ENED, and EDEN) of substrate radical anion-induced electrocarboxylation are discussed, which differ in their electron transfer sequence, substrate dissociation, and nucleophilic reaction, to highlight their implications on reactivity and product selectivity.
Implant-associated infections caused by biomedical catheters severely threaten patientsʼ health. The use of electrochemical control on NO release from benign nitrite equipped in the catheter can potentially resolve this issue with excellent biocompatibility. Inspired by nitrite reductase, a Cu-BDC (BDC: benzene-1,4-dicarboxylic acid) catalyst with coordinated Cu(II) sites was constructed as a heterogeneous electrocatalyst to control nitrite reduction to nitric oxide for catheter antibacteria. The combined results of in situ and ex situ tests unveil the key function of interconversion between Cu(II) and Cu(I) species in NO2 − reduction to NO. After being incorporated into the actual catheter, the Cu-BDC catalyst exhibits high electrocatalytic activity toward NO2 − reduction to NO and excellent antibacteria efficacy with a sterilizing rate of 99.9%, paving the way for the development of advanced metal–organic frameworks (MOFs) electrocatalysts for catheter antibacteria.
Vanadium flow batteries (VFBs) are considered ideal for grid-scale, long-duration energy storage applications owing to their decoupled output power and storage capacity, high safety, efficiency, and long cycle life. However, the widespread adoption of VFBs is hindered by the use of expensive Nafion membranes. Herein, we report a soft template-induced method to develop a porous polyvinylidene fluoride (PVDF) membrane for VFB applications. By incorporating water-soluble and flexible polyethylene glycol (PEG 400) as a soft template, we induced the aggregation of hydrophilic sulfonated poly (ether ether ketone), resulting in phase separation from the hydrophobic PVDF polymer during membrane formation. This process led to the creation of a porous PVDF membrane with controllable morphologies determined by the polyethylene glycol content in the cast solution. The optimized porous PVDF membrane enabled a stable VFB performance for 200 cycles at a current density of 80 mA/cm2, and the VFB exhibited a Coulombic efficiency of 95.2% and a voltage efficiency of 87.8%. These findings provide valuable insights for the development of highly stable membranes for VFB applications.
The interaction between a promoter and an active metal crucially impacts catalytic performance. Nowadays, the influence of promoter contents and species has been intensively considered. In this study, we investigate the effect of the iron (Fe)–zinc (Zn) proximity of Fe–Zn bimetallic catalysts on CO2 hydrogenation performance. To eliminate the size effect, Fe2O3 and ZnO nanoparticles with uniform size are first prepared by the thermal decomposition method. By changing the loading sequence or mixing method, a series of Fe–Zn bimetallic catalysts with different Fe–Zn distances are obtained. Combined with a series of characterization techniques and catalytic performances, Fe–Zn bimetallic proximity for compositions of Fe species is discussed. Furthermore, we observe that a smaller Fe–Zn distance inhibits the reduction and carburization of the Fe species and facilitates the oxidation of carbides. Appropriate proximity of Fe and Zn (i.e., Fe1Zn1-imp and Fe1Zn1-mix samples) results in a suitable ratio of the Fe5C2 and Fe3O4 phases, simultaneously promoting the reverse water–gas shift and Fischer–Tropsch synthesis reactions. This study provides insight into the proximity effect of bimetallic catalysts on CO2 hydrogenation performance.
The lattice oxygen oxidation mechanism (LOM) provides an efficient pathway for accelerating the oxygen evolution reaction (OER) in certain electrocatalysts by activating and involving lattice oxygen in the catalytic OER process. We investigated the potential of disordered rocksalts as catalysts for accelerating the OER through the LOM process, leveraging their unique metastable Li–O–Li bond states. Theoretical calculations were employed to predict the catalytic pathways and activities of disordered rocksalts (DRX), such as Li1.2Co0.4Ti0.5O2 (LCTO). The results revealed that benefiting from the unhybridized Li–O electronic orbitals and the resulting metastable states of Li–O–Li bonds in DRX, LCTO exhibited a typical LOM pathway, and the lattice oxygen was easily activated and participated in the OER. The experimental results showed that LCTO exhibited a remarkable pH-dependent OER activity through the LOM pathway, with an overpotential of 241 mV at a current density of 10 mA/cm2, and excellent long-term stability. This work provides a novel chemical space for designing highly active and stable OER electrocatalysts by leveraging the LOM reaction pathway.