The reasonable design of electrode materials for rechargeable batteries plays an important role in promoting the development of renewable energy technology. With the in-depth understanding of the mechanisms underlying electrode reactions and the rapid development of advanced technology, the performance of batteries has significantly been optimized through the introduction of defect engineering on electrode materials. A large number of coordination unsaturated sites can be exposed by defect construction in electrode materials, which play a crucial role in electrochemical reactions. Herein, recent advances regarding defect engineering in electrode materials for rechargeable batteries are systematically summarized, with a special focus on the application of metal-ion batteries, lithium-sulfur batteries, and metal-air batteries. The defects can not only effectively promote ion diffusion and charge transfer but also provide more storage/adsorption/active sites for guest ions and intermediate species, thus improving the performance of batteries. Moreover, the existing challenges and future development prospects are forecast, and the electrode materials are further optimized through defect engineering to promote the development of the battery industry.

Defect Engineering on Electrode Materials for Rechargeable Batteries.

The electrocatalytic CO2 reduction reaction (CRR) and N2 reduction reaction (NRR), which convert inert small molecules into high-value products under mild conditions, have received much research attention Defect engineering is an important strategy for modulating the electronic properties of electrocatalysts, which may endow unexpected physical and chemical properties to break the intrinsic bottleneck and, therefore, boost the electrocatalytic performance To date, various defective nanomaterials (such as nanocarbon and transition metal compounds) have been synthesized that display great potential for the CRR and NRR Therefore, a deep understanding of the influence of defects on the catalytic activity is urgently needed In this review, the type, regulation strategy, fine defect characterization methods, and their application in the electrocatalytic CRR and NRR are discussed and summarized Furthermore, the major challenges, opportunities, and future development direction of defect engineering in CRR and NRR catalysts are proposed This review aims to provide a reference for the proof-of-concept design of highly active CRR and NRR electrocatalysts

Defect engineering in earth-abundant electrocatalysts for CO2 and N2 reduction

The commercialization of fuel cells, such as proton exchange membrane fuel cells and direct methanol/formic acid fuel cells, is hampered by their poor stability, high cost, fuel crossover, and the sluggish kinetics of platinum (Pt) and Pt-based electrocatalysts for both the cathodic oxygen reduction reaction (ORR) and the anodic hydrogen oxidation reaction (HOR) or small molecule oxidation reaction (SMOR). Thus far, the exploitation of active and stable electrocatalysts has been the most promising strategy to improve the performance of fuel cells. Accordingly, increasing attention is being devoted to modulating the surface/interface electronic structure of electrocatalysts and optimizing the adsorption energy of intermediate species by defect engineering to enhance their catalytic performance. Defect engineering is introduced in terms of defect definition, classification, characterization, construction, and understanding. Subsequently, the latest advances in defective electrocatalysts for ORR and HOR/SMOR in fuel cells are scientifically and systematically summarized. Furthermore, the structure-activity relationships between defect engineering and electrocatalytic ability are further illustrated by coupling experimental results and theoretical calculations. With a deeper understanding of these complex relationships, the integration of defective electrocatalysts into single fuel-cell systems is also discussed. Finally, the potential challenges and prospects of defective electrocatalysts are further proposed, covering controllable preparation, in situ characterization, and commercial applications.

Defect Engineering for Fuel‐Cell Electrocatalysts

Life science and energy conversion have been becoming the two major themes in 21st century considering the increasing awareness of disease prevention and overuse of fossil fuels. Therefore, how to understand the evolution mechanisms of single cells and the fundamental pathways of clean energy conversion have become significant matters of utmost urgency. Electrochemical measurement is a powerful analytical method that has been used for a wide range of applications including detecting faint bioelectricity and evaluating novel electrocatalysts. Nevertheless, conventional electrochemical techniques suffer from limited sensitivity due to the interference of charging/discharging current and side reactions. As a branch of electrochemical technologies, however, electrochemiluminescence (ECL) possesses high sensitivity and broad dynamic range by the transformation of input electrical signal into optical readout, which differs from most other electrochemical techniques. In fact, ECL relies on the generation of elec...

Recent Progress in Electrochemiluminescence Sensing and Imaging.

Among the various energy storage systems, the rechargeable Zn–air battery is one of the most promising candidates for the consumer electronic market and portable energy sources. In a Zn–air battery, surface/interface chemistry plays a key role in their performance optimization of power density, stability and rechargeable efficiency. A Zn–air battery requires gas-involved ORR (oxygen reduction reaction) and OER (oxygen evolution reaction) reactions, always leading to complex reactions and sluggish kinetic processes at the three-phase interface, in which rational surface/interface nanoengineering at the micro and meso-level play a decisive role. In this review, we cover the influence of surface/interface properties of electrocatalysts and air electrodes on the performance of rechargeable Zn–air batteries, and the latest surface/interface nanoengineering progress from the micro to meso-level is surveyed. Moreover, the surface/interface characteristics of electrocatalysts and air electrodes at the triple-phase interface, which are closely related to the four key parameters of electrical conductivity, reaction energy barrier, reaction surface area and mass transfer behavior, are also described in detail. Based on the discussion of the latest achievements of surface/interface nanoengineering, some personal perspectives on future advanced development of rechargeable Zn–air batteries are presented as well.

Surface/interface nanoengineering for rechargeable Zn–air batteries

Electrocatalysis is dominated by reaction at the solid-liquid-gas interface; surface properties of electrocatalysts determine the electrochemical behavior. The surface charge of active sites on catalysts modulate adsorption and desorption of intermediates. However, there is no direct evidence to bridge surface charge and catalytic activity of active sites. Defects (active sites) were created on a HOPG (highly oriented pyrolytic graphite) surface that broke the intrinsic sp2 -hybridization of graphite by plasma, inducing localization of surface charge onto defective active sites, as shown by scanning ion conductance microscopy (SICM) and Kelvin probe force microscopy (KPFM). An electrochemical test revealed enhanced intrinsic activity by the localized surface charge. DFT calculations confirmed the relationship between surface charge and catalytic activity. This work correlates surface charge and catalytic activity, providing insights into electrocatalytic behavior and guiding the design of advanced electrocatalysts.

Bridging the Surface Charge and Catalytic Activity of a Defective Carbon Electrocatalyst.

Electrochemiluminescence (ECL)-based capacitance microscopy using a square-wave voltage is established unprecedentedly to realize the label-free visualization of species on electrode surfaces and cellular plasma membranes. The drop in the local capacitance upon the binding of species to the surface or to a cellular membrane is derived to induce a relatively larger potential drop ( Vdl) across the double layer on the local electrode surface, which is utilized to prompt enhanced ECL at the binding position. The square-wave voltage with a frequency of as high as 1.5 kHz is proven to be favorable for the discrimination of the local ECL from the surrounding signal. Using this new detection principle and resultant capacitance microscopy, carcinoembryonic antigens (CEA) at amounts of as low as 1 pg can be visualized. Further application of this approach permits the direct imaging of CEA antigens on single MCF-7 cells through the capacitance change after the formation of the antigen-antibody complex. Successful visualization of the analyte without any ECL tag will allow not only special capacitance microscopy for label-free bioassays but also a novel ECL detection approach for the sensitive detection of biomolecules.

Electrochemiluminescence-Based Capacitance Microscopy for Label-Free Imaging of Antigens on the Cellular Plasma Membrane

The inside walls of a nanopipette tip are decorated by a Pt deposit that is used as an open bipolar electrochemiluminescence (ECL) device to achieve intracellular wireless electroanalysis. The synergetic actions of nanopipette and of bipolar ECL lead to the spatial confinement of the voltage drop at the level of the Pt deposit, which generates ECL emission from luminol. The porous structure of Pt deposit permits the electrochemical transport of intracellular molecules into the nanopipette that is coupled with enzymatic reactions. Thus, the intracellular concentrations of hydrogen peroxide or glucose are measured in vivo as well as the intracellular sphingomyelinase activity. In comparison with the classic bipolar ECL, the remarkably low potential applied in our approach is restricted inside the nanopipette and it minimizes the potential bias of the voltage on the cellular activity. Accordingly, this wireless ECL approach provides a new direction for analysis of single living cells.

Intracellular Wireless Analysis of Single Cells by Bipolar Electrochemiluminescence Confined in a Nanopipette.

In this letter, in situ imaging of the photocatalytic activity of titanium dioxide (TiO2) nanotubes for the degradation of an organic pollutant (i.e., Rhodamine B (RhB)) is realized with nanometer resolution using scanning ion conductance microscopy (SICM). Upon illumination, the separated electrons and holes at the nanotubes induce oxidation of RhB to produce the more positively charged Rhodamine 123 (Rh 123), which leads to increased ionic current through the capillary orifice and an elevated apparent altitude in the SICM image. Active sites with higher activity on the nanotubes exhibit a significant high spatial-resolution character. The successful imaging of the photocatalytic activity of TiO2 nanotubes should provide an in situ approach for local investigation of the photocatalytic process at the catalyst.

In Situ Imaging of Photocatalytic Activity at Titanium Dioxide Nanotubes Using Scanning Ion Conductance Microscopy

The pursuit of strong electrochemiluminescence (ECL) at a low voltage is crucial, but challenging, for further development of ECL based bioanalysis, especially at single cells. In this work, single lithium iron phosphate (LiFePO4, LFP) nanoparticles at the surface of indium tin oxide (ITO) is firstly applied to produce enhanced ECL from luminol and hydrogen peroxide under a low voltage of 0.5 V. Lithium ions from single LFP particles are proposed to be de-intercalated during the charging process and then inserted into ITO to form LiSnO2, in which the oxidation of a luminol derivative (L012) is promoted resulting in an ECL emission at a low voltage. Meanwhile, the transformation of LiFePO4 into FePO4 under this voltage accelerates the generation of oxygen intermediates from hydrogen peroxide, and thus, leads to an elevated ECL intensity. Eventually, the efflux of hydrogen peroxide from single living cells is directly visualized under a voltage of 0.5 V using the ECL imaging approach, which is significantly lower than the previous voltage of 1.0 V. The first coupling of lithium migration in ECL reaction will pave a new direction to improve the ECL emission efficiency, and ultimately, push the development of ECL technology in highly spatial sensing of single cells.

Enhanced electrochemiluminescence at single lithium iron phosphate nanoparticles for the local sensing of hydrogen peroxide efflux from single living cell under a low voltage

Rong Jin

Papers

Bridging the Surface Charge and Catalytic Activity of a Defective Carbon Electrocatalyst.

Electrochemiluminescence-Based Capacitance Microscopy for Label-Free Imaging of Antigens on the Cellular Plasma Membrane

Intracellular Wireless Analysis of Single Cells by Bipolar Electrochemiluminescence Confined in a Nanopipette.

In Situ Imaging of Photocatalytic Activity at Titanium Dioxide Nanotubes Using Scanning Ion Conductance Microscopy

Enhanced electrochemiluminescence at single lithium iron phosphate nanoparticles for the local sensing of hydrogen peroxide efflux from single living cell under a low voltage