Free Electrons to Molecular Bonds and Back: Closing the Energetic Oxygen Reduction (ORR)-Oxygen Evolution (OER) Cycle Using Core-Shell Nanoelectrocatalysts

Recent advances in electrochemical non-enzymatic glucose sensors - A review

This review encompasses the mechanisms of electrochemical glucose detection and recent advances in non-enzymatic glucose sensors based on a variety of materials ranging from platinum, gold, metal alloys/adatom, non-precious transition metal/metal oxides to glucose-specific organic materials. It shows that the discovery of new materials based on unique nanostructures have not only provided the detailed insight into non-enzymatic glucose oxidation, but also demonstrated the possibility of direct detection in whole blood or interstitial fluids. We critically evaluate various aspects of non-enzymatic electrochemical glucose sensors in terms of significance as well as performance. Beyond laboratory tests, the prospect of commercialization of non-enzymatic glucose sensors is discussed.

Advanced Architectures and Relatives of Air Electrodes in Zn-Air Batteries

Zn-air batteries are becoming the promising power sources for portable and wearable electronic devices and hybrid/electric vehicles because of their high specific energy density and the low cost for next-generation green and sustainable energy technologies. An air electrode integrated with an oxygen electrocatalyst is the most important component and inevitably determines the performance and cost of a Zn-air battery. This article presents exciting advances and challenges related to air electrodes and their relatives. After a brief introduction of the Zn-air battery, the architectures and oxygen electrocatalysts of air electrodes and relevant electrolytes are highlighted in primary and rechargeable types with different configurations, respectively. Moreover, the individual components and major issues of flexible Zn-air batteries are also highlighted, along with the strategies to enhance the battery performance. Finally, a perspective for design, preparation, and assembly of air electrodes is proposed for the future innovations of Zn-air batteries with high performance.

The role of carbonate in electro-catalytic water oxidation by using Ni(1,4,8,11-tetraazacyclotetradecane)2

NiL_i²⁺ are good electro-catalysts for water oxidation in phosphate or carbonate buffers. The results point out that the active oxidizing agents are L(X)Ni^IVOH^{4-(3-n+1)/(2-n+1)}, where X = PO₄H_n^(3-n)- or CO₃H_n^(2-n)- formed from LNi^IVX₂via a mechanism involving an acid catalyzed O-P or O-C bond heterolysis. Carbonate behaves differently from phosphate as it is a non-innocent ligand and it can be oxidized.

Ternary PtVCo dendrites for the hydrogen evolution reaction, oxygen evolution reaction, overall water splitting and rechargeable Zn–air batteries

Designing a highly active, robust and cost-effective electrocatalyst with multiple functionalities toward overall water splitting and rechargeable Zn–air battery applications is crucial and urgent for the development of sustainable energy sources.

Unprecedented carbon sub-microspheres with a porous hierarchy for highly efficient oxygen electrochemistry

Developing efficient and robust electrocatalysts for bifunctional oxygen electrocatalysis is crucial for renewable energy technology. Herein, nitrogen and phosphorus co-doped carbon sub-microspheres with fascinating mesostructures are rationally synthesized through an effective soft-templating strategy. The unique features of substantial doping, large surface areas and well-defined porosity endow the dual-doped carbons with high-density electroactive sites, considerable active surface areas and improved mass transfer, ensuring impressive activity and durability in catalyzing oxygen reduction and evolution reactions, even competing with the noble metal benchmarks, thus assuring their use as an air cathode in a rechargeable Zn-air battery with low charge-discharge overpotential and remarkable long-term stability.

Mechanistic Studies on the Role of [CuII (CO3 )n ]2-2n as a Water Oxidation Catalyst: Carbonate as a Non-Innocent Ligand

Recently it was reported that copper bicarbonate/carbonate complexes are good electro-catalysts for water oxidation. However, the results did not enable a decision whether the active oxidant is a Cu^III or a Cu^IV complex. Kinetic analysis of pulse radiolysis measurements coupled with DFT calculations point out that Cu^III (CO₃ )_n^3-2n complexes are the active intermediates in the electrolysis of Cu^II (CO₃ )_n^2-2n solution. The results enable the evaluation of E°[(Cu^III/II (CO₃ )_n )_aq ]≈1.42 V versus NHE at pH 8.4. This redox potential is in accord with the electrochemical report. As opposed to literature suggestions for water oxidation, the present results rule out single-electron transfer from Cu^III (CO₃ )_n^3-2n to yield hydroxyl radicals. Significant charge transfer from the coordinated carbonate to Cu^III results in the formation of C₂ O₆^2- by means of a second-order reaction of Cu^III (CO₃ )_n^3-2n . The results point out that carbonate stabilizes transition-metal cations at high oxidation states, not only as a good sigma donor, but also as a non-innocent ligand.

CoSex nanocrystalline-dotted CoCo layered double hydroxide nanosheets: a synergetic engineering process for enhanced electrocatalytic water oxidation

Manipulating the electrical conductivity and morphology of Co-based (hydr)oxides is significant for optimizing energy conversion in the oxygen evolution reaction (OER). Herein, 2D CoSe_x nanocrystalline-dotted porous CoCo layered double hydroxide nanosheets (Co-Se NSs) were designed and synthesized via a modified in situ reduction and interface-directed assembly in an inert atmosphere. During the synchronous reduction/precipitation reaction between Co²⁺-oleylamine and NaHSe at the toluene-water interface, the hydrated Co-O and Co-Se clusters are generated and sequentially assemble under strong extrusion driven by the interfacial tension. Owing to the enriched vacancies on the lateral surfaces, the obtained loose and porous Co-Se NS presents low crystallinity. Moreover, electrons could spontaneously transfer from the CoCo LDH to the neighboring CoSe_x nanocrystallites due to the stronger electron-withdrawing capability of metallic CoSe_x, and thus more Co atoms in the CoCo layered double hydroxide (LDH) present a high oxidation state. This synergistic manipulation in the structure, component, and electron configuration of the Co-Se NS can increase the density of the OER active-sites, improve the electrical conductivity, and also offer a large accessible surface area and permeable channels for ion adsorption and transport. As a result, the resulting Co-Se NSs feature high catalytic activity towards OER, in particular a low onset potential of 1.48 V and an overpotential of only 290 mV at a current density of 10 mA cm^-2 for the Co-Se-2 NS, as well as good stability in an accelerated durability test. The strategy developed here provides a reliable and valid way to synthesize multicomponent NSs, and is able to be extended to other areas of application.

Imaging Dynamic Collision and Oxidation of Single Silver Nanoparticles at the Electrode/Solution Interface

The electrochemical interface is an ultrathin interfacial region between the electrode surface and the electrolyte solution and is often characterized by numerous dynamic processes, such as solvation and desolvation, heterogeneous electron transfer, molecular adsorption and desorption, diffusion, and surface rearrangement. Many of these processes are driven and modulated by the presence of a large interfacial potential gradient. The study and better understanding of the electrochemical interface is important for designing better electrochemical systems where their applications may include batteries, fuel cells, electrocatalytic water splitting, corrosion protection, and electroplating. This, however, has proved to be a challenging analytical task due to the ultracompact and dynamic evolving nature of the electrochemical interface. Here, we describe the use of an electrochemical nanocell to image the dynamic collision and oxidation process of single silver nanoparticles at the surface of a platinum nanoelectrode. A nanocell is prepared by depositing a platinum nanoparticle at the tip of a quartz nanopipette forming a bipolar nanoelectrode. The compact size of the nanocell confines the motion of the silver nanoparticle in a 1-D space. The highly dynamic process of nanoparticle collision and oxidation is imaged by single-particle fluorescence microscopy. Our results demonstrate that silver nanoparticle collision and oxidation is highly dynamic and likely controlled by a strong electrostatic effect at the electrode/solution interface. We believe that the use of a platinum nanocell and single molecule/nanoparticle fluorescence microscopy can be extended to other systems to yield highly dynamic information about the electrochemical interface.

Pt/Co Alloy Nanoparticles Prepared by Nanocapsule Method Exhibit a High Oxygen Reduction Reaction Activity in the Alkaline Media

Oxygen reduction reaction (ORR) catalysts are one of the main topics for fuel cells and metal/air batteries. We found that the platinum-cobalt alloy nanoparticles prepared by our original nanocapsule method exhibited a high ORR catalytic activity in alkaline solution, compared with that of the existing alloy nanoparticles prepared by different methods. The effect of alloy composition on the ORR activity was investigated to find the optimum composition (approximately 40 atom %). We also found that the enhancement of the catalytic activity in alkaline solution appeared in a very narrow range of Co content compared with that in acidic solution.

Impacts of interfacial charge transfer on nanoparticle electrocatalytic activity towards oxygen reduction

Interfacial electron transfer within platinum and non-platinum-based nanocatalysts plays a significant role in the manipulation of the electronic interactions between oxygen species and the catalyst surfaces, which may be exploited as an effective mechanism to enhance and optimize the activity towards oxygen reduction.

Grand challenges for catalysis in the Science and Technology Roadmap on Catalysis for Europe: moving ahead for a sustainable future

This perspective discusses the general concepts that will guide future catalysis and related grand challenges based on the Science and Technology Roadmap on Catalysis for Europe prepared by the European Cluster on Catalysis.