Oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are the two most important reactions in rechargeable metal‐air battery, a promising technology to meet the energy requirements for various applications. The development of low‐cost, highly efficient and stable bifunctional ORR/OER catalysts is critical for a large‐scale application of this technology. In this review, the authors first introduce the fundamentals of bifunctional ORR/OER electrocatalysis in alkaline electrolyte. Various types of nanostructured materials as bifunctional ORR/OER catalysts including metal oxide, hydroxide and sulfide, functional carbon material, metal, and their composites are then reviewed. The crucial factors that can be used to tune the activity of the catalyst towards ORR/OER are summarized, including (1) phase, morphology, crystal facet, defect, mixed‐metal and strain engineering for metal oxide; (2) heteroatom doping, topological defects, and formation of metal‐N‐C structure for carbon material; (3) alloy effect for metal. These experiences lay the foundation for large scale application of metal‐air battery and can also effectively guide the rational design of catalysts for other electrocatalytic reactions.

The vision of a hydrogen economy relies on efficient utilization and production of hydrogen in a hydrogen fuel cell and a water electrolyzer. In both technologies, the sluggish kinetics of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) account for the most efficiency loss because the reactions on catalytic sites are constrained by adsorption-energy scaling relations involving intermediates of *OOH, *O, and *OH (where * denotes the active site). Therefore, a novel paradigm for catalyst design is required by overcoming or circumventing the adsorption-energy scaling relations. In this Review, the fundamentals of oxygen electrocatalysis, including reaction of the mechanism and origin of the adsorption-energy scaling relationship, are first introduced. Crucial strategies to overcome the scaling relations are then summarized. Finally, future research directions in this area are proposed. This work provides guidelines for the rational design of efficient catalysts for oxygen electrocatalysis beyond the limitation posed by scaling relations.

This article reports on a noninvasive approach in detecting and following-up individuals who are at-risk or have an existing COVID-19 infection, with a potential ability to serve as an epidemic control tool. The proposed method uses a developed breath device composed of a nanomaterial-based hybrid sensor array with multiplexed detection capabilities that can detect disease-specific biomarkers from exhaled breath, thus enabling rapid and accurate diagnosis. An exploratory clinical study with this approach was examined in Wuhan, China, during March 2020. The study cohort included 49 confirmed COVID-19 patients, 58 healthy controls, and 33 non-COVID lung infection controls. When applicable, positive COVID-19 patients were sampled twice: during the active disease and after recovery. Discriminant analysis of the obtained signals from the nanomaterial-based sensors achieved very good test discriminations between the different groups. The training and test set data exhibited respectively 94% and 76% accuracy in differentiating patients from controls as well as 90% and 95% accuracy in differentiating between patients with COVID-19 and patients with other lung infections. While further validation studies are needed, the results may serve as a base for technology that would lead to a reduction in the number of unneeded confirmatory tests and lower the burden on hospitals, while allowing individuals a screening solution that can be performed in PoC facilities. The proposed method can be considered as a platform that could be applied for any other disease infection with proper modifications to the artificial intelligence and would therefore be available to serve as a diagnostic tool in case of a new disease outbreak.

Electrochemical reduction of CO2 could mitigate environmental problems originating from CO2 emission. Although grain boundaries (GBs) have been tailored to tune binding energies of reaction intermediates and consequently accelerate the CO2 reduction reaction (CO2RR), it is challenging to exclusively clarify the correlation between GBs and enhanced reactivity in nanostructured materials with small dimension (<10 nm). Now, sub‐2 nm SnO2 quantum wires (QWs) composed of individual quantum dots (QDs) and numerous GBs on the surface were synthesized and examined for CO2RR toward HCOOH formation. In contrast to SnO2 nanoparticles (NPs) with a larger electrochemically active surface area (ECSA), the ultrathin SnO2 QWs with exposed GBs show enhanced current density (j), an improved Faradaic efficiency (FE) of over 80 % for HCOOH and ca. 90 % for C1 products as well as energy efficiency (EE) of over 50 % in a wide potential window; maximum values of FE (87.3 %) and EE (52.7 %) are achieved.

Electrochemical CO 2 reduction relies on the availability of highly efficient and selective catalysts.H erein, we report ageneral strategy to boost the activity of metal-organic frameworks (MOFs) towardsC O 2 reduction via ligand doping. As trong electron-donating molecule of 1,10-phenanthroline was doped into Zn-based MOFs of zeolitic imidazolate framework-8 (ZIF-8) as CO 2 reduction electrocatalyst. Experimental and theoretical evidences reveal that the electron-donating nature of phenanthroline enables ac harge transfer,w hichi nduces adjacent active sites at the sp 2 C atoms in the imidazole ligand possessing more electrons,a nd facilitates the generation of *COOH, hence leading to improved activity and Faradaic efficiency towards CO production.Carbon dioxide conversion using electrochemical approaches to obtain high value-added products has been regarded as ap romising strategy to recycle and utilize this abundant and inexpensive carbon resource. [1] However, due to the thermodynamically stable and kinetically inert nature of CO 2 ,a sw ell as the competing reaction of hydrogen evolution reaction (HER) in aqueous electrolyte,h ighly efficient and selective electrocatalysts are crucial in this endeavor. [2] As at ypical product of CO 2 reduction, CO is important for synthesizing more complex carbon-based fuels and feedstocks,w hich holds great significance for the chemical industry. [3] Low-cost and earth-abundant transition-metal based nanomaterials,such as Co, [4] Ni, [5] Cu, [6] and Zn, [7] have been widely investigated to electrochemically catalyze CO 2 reduction reaction (CO 2 RR) to produce CO during the recent years.Metal-organic based complexes and frameworks,w ith accurate molecular structures,a nd well-dispersed metal center, have exhibited promising activity in electrocatalysis. [8] Among these kinds of metal-organic based catalysts,t he metal centers usually act as catalytic active sites.However,it is of note that the main electrocatalytic active sites in Znbased complexes or metal-organic frameworks (MOFs) are usually not the metal center for CO 2 RR process,owing to the fully occupied 3d orbital of Zn II ,but the ligands coordinating with the Zn centers. [9] This bestows new opportunities to optimize the electrocatalytic activity by tuning the ligand itself.F rom another aspect, it has been shown that an electron-rich active center could facilitate CO 2 molecule activation by enhancing electron movement from the active sites to the antibonding orbitals of CO 2 and coupling with protons generating *COOH (the key intermediate for CO production). [7c, 10] Thus,i ncreasing the charge density on the catalytic sites would be ap romising strategy to enhance CO 2 RR activity.T ot his end, we propose an ew strategy to induce more electron density on the ligand sites of ZIFs by apost-treatment process.Byv irtue of ligand doping process, an ew ligand with strong electron-donating ability could act on the MOFs to induce more charge density on the adjacent original ligand sites,s ubsequently enhancing the...