Nafion/lead oxide–manganese oxide combined catalyst for use as a highly efficient alkaline air electrode in zinc–air battery

Self-Assembly of Surface-Functionalized Ag1.8 Mn8 O16 Nanorods with Reduced Graphene Oxide Nanosheets as an Efficient Bifunctional Electrocatalyst for Rechargeable Zinc-Air Batteries

Bifunctional electrocatalysts play a key role in the performance of rechargeable metal-air batteries. Herein, we report a hybrid catalyst, Ag_1.8 Mn₈ O₁₆ /rGO, self-assembled by Ag_1.8 Mn₈ O₁₆ nanorods and reduced graphene oxide (rGO) nanosheets through electrostatic attraction. The hybrid catalyst exhibits a better oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) activity than commercial Pt/C in alkaline medium. When employed as an air-cathode catalyst in Zn-air cells, the hybrids enabled higher and more stable output voltage and better durability of the cells, benefitting from the improved electrode conductivity, larger surface area, and synergetic coupling as a result of its high structural integrity.

Silver Decorated Reduced Graphene Oxide as Electrocatalyst for Zinc–Air Batteries

Due to their low cost and very high energy density, zinc–air batteries (ZABs) exhibit high potential for various energy applications. The electrochemical performance of the air-cathode has a decisive impact on the discharge performance of ZABs because the sluggish oxygen reduction reaction (ORR) kinetics increase the overpotential of the air-cathode and hence the performance of ZABs. In this work, reduced graphene oxide decorated with silver nanoparticles (AgNP/rGO) is synthesized using simultaneous reduction of graphene oxide and silver ions. Different amounts of silver loading are examined for the synthesis of AgNP/rGO. The synthesized AgNP/rGO samples are analyzed using a rotating disk electrode in order to investigate ORR activity. Then, the synthesized AgNP/rGO electrocatalyst is applied on a tubular designed zinc–air battery in order to study the performance of the zinc–air battery. Results demonstrate that AgNP/rGO is an efficient and cost-effective ORR electrocatalyst for its practical application in ZABs.

Co3O4/MnO2/Hierarchically Porous Carbon as Superior Bifunctional Electrodes for Liquid and All-Solid-State Rechargeable Zinc-Air Batteries

The design of efficient, durable, and affordable catalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is very indispensable in liquid-type and flexible all-solid-state zinc-air batteries. Herein, we present a high-performance bifunctional catalyst with cobalt and manganese oxides supported on porous carbon (Co₃O₄/MnO₂/PQ-7). The optimized Co₃O₄/MnO₂/PQ-7 exhibited a comparable ORR performance with commercial Pt/C and a more superior OER performance than all of the other prepared catalysts, including commercial Pt/C. When applied to practical aqueous (6.0 M KOH) zinc-air batteries, the Co₃O₄/MnO₂/porous carbon hybrid catalysts exhibited exceptional performance, such as a maximum discharge peak power density as high as 257 mW cm^-2 and the most stable charge-discharge durability over 50 h with negligible deactivation to date. More importantly, a series of flexible all-solid-state zinc-air batteries can be fabricated by the Co₃O₄/MnO₂/porous carbon with a layer-by-layer method. The optimal catalyst (Co₃O₄/MnO₂/PQ-7) exhibited an excellent peak power density of 45 mW cm^-2. The discharge potentials almost remained unchanged for 6 h at 5 mA cm^-2 and possessed a long cycle life (2.5 h@5 mA cm^-2). These results make the optimized Co₃O₄/MnO₂/PQ-7 a promising cathode candidate for both liquid-type and flexible all-solid-state zinc-air batteries.

An electrochemical immunosensor based on a 3D carbon system consisting of a suspended mesh and substrate-bound interdigitated array nanoelectrodes for sensitive cardiac biomarker detection

We developed an electrochemical redox cycling-based immunosensor using a 3D carbon system consisting of a suspended mesh and substrate-bound interdigitated array (IDA) nanoelectrodes. The carbon structures were fabricated using a simple, cost-effective, and reproducible microfabrication technology known as carbon microelectromechanical systems (C-MEMS). We demonstrated that the 3D sub-micrometer-sized mesh architecture and selective modification of the suspended mesh facilitated the efficient production of large quantities of electrochemical redox species. The electrochemically active surfaces and small size of IDA nanoelectrodes with a 1:1 aspect ratio exhibited high signal amplification resulting from efficient redox cycling of electrochemical species (PAP/PQI) by a factor of ~25. The proposed selective surface modification scheme facilitated efficient redox cycling and exhibited a linear detection range of 0.001-100 ng/mL for cardiac myoglobin (cMyo). The specific detection of cMyo was also achieved in the presence of other interfering species. Moreover, the proposed 3D carbon system-based immunosensor successfully detected as low as ~0.4 pg/mL cMyo in phosphate-buffered saline and human serum.

Graphene aerogel-supported and graphene quantum dots-modified γ-MnOOH nanotubes as a highly efficient electrocatalyst for oxygen reduction reaction

In this work, we demonstrate a facile strategy to synthesize a novel three-dimensional (3D) graphene aerogel-supported and graphene quantum dots-modified γ-MnOOH nanotubes as a highly efficient electrocatalyst.

Co3O4 nanoparticles decorated carbon nanofiber mat as binder-free air-cathode for high performance rechargeable zinc-air batteries

An efficient, durable and low cost air-cathode is essential for a high performance metal-air battery for practical applications. Herein, we report a composite bifunctional catalyst, Co3O4 nanoparticles-decorated carbon nanofibers (CNFs), working as an efficient air-cathode in high performance rechargeable Zn-air batteries (ZnABs). The particles-on-fibers nanohybrid materials were derived from electrospun metal-ion containing polymer fibers followed by thermal carbonization and a post annealing process in air at a moderate temperature. Electrochemical studies suggest that the nanohybrid material effectively catalyzes oxygen reduction reaction via an ideal 4-electron transfer process and outperforms Pt/C in catalyzing oxygen evolution reactions. Accordingly, the prototype ZnABs exhibit a low discharge-charge voltage gap (e.g. 0.7 V, discharge-charge at 2 mA cm(-2)) with higher stability and longer cycle life compared to their counterparts constructed using Pt/C in air-cathode. Importantly, the hybrid nanofiber mat readily serves as an integrated air-cathode without the need of any further modification. Benefitting from its efficient catalytic activities and structural advantages, particularly the 3D architecture of highly conductive CNFs and the high loading density of strongly attached Co3O4 NPs on their surfaces, the resultant ZnABs show significantly improved performance with respect to the rate capability, cycling stability and current density, promising good potential in practical applications.

Bismuth oxide nanoparticles as a nanoscale guide to form a silver–polydopamine hybrid electrocatalyst with enhanced activity and stability for the oxygen reduction reaction

High dispersion Ag nanoparticles were successfully synthesized on functionalized polydopamine@Bi₂O₃ NPs for use as electrocatalyst. Synergetic effect was found to enhance the catalytic ability for direct 4e⁻ transfer in oxygen reduction reaction.

Electrochemical signal amplification for immunosensor based on 3D interdigitated array electrodes

We devised an electrochemical redox cycling based on three-dimensional interdigitated array (3D IDA) electrodes for signal amplification to enhance the sensitivity of chip-based immunosensors. The 3D IDA consists of two closely spaced parallel indium tin oxide (ITO) electrodes that are positioned not only on the bottom but also the ceiling, facing each other along a microfluidic channel. We investigated the signal intensities from various geometric configurations: Open-2D IDA, Closed-2D IDA, and 3D IDA through electrochemical experiments and finite-element simulations. The 3D IDA among the four different systems exhibited the greatest signal amplification resulting from efficient redox cycling of electroactive species confined in the microchannel so that the faradaic current was augmented by a factor of ∼100. We exploited the enhanced sensitivity of the 3D IDA to build up a chronocoulometric immunosensing platform based on the sandwich enzyme-linked immunosorbent assay (ELISA) protocol. The mouse IgGs on the 3D IDA showed much lower detection limits than on the Closed-2D IDA. The detection limit for mouse IgG measured using the 3D IDA was ∼10 fg/mL, while it was ∼100 fg/mL for the Closed-2D IDA. Moreover, the proposed immunosensor system with the 3D IDA successfully worked for clinical analysis as shown by the sensitive detection of cardiac troponin I in human serum down to 100 fg/mL.

Co3O4 nanoparticle-modified MnO2 nanotube bifunctional oxygen cathode catalysts for rechargeable zinc-air batteries

We report the preparation of MnO2 nanotubes functionalized with Co3O4 nanoparticles and their use as bifunctional air cathode catalysts for oxygen reduction reaction and oxygen evolution reaction in rechargeable zinc-air batteries. These hybrid MnO2/Co3O4 nanomaterials exhibit enhanced catalytic reactivity toward oxygen evolution reaction under alkaline conditions compared with that in the presence of MnO2 nanotubes or Co3O4 nanoparticles alone.

Room temperature aerobic oxidation of amines by a nanocrystalline ruthenium oxide pyrochlore nafion composite catalyst

The aerobic oxidation of primary amines to their respective nitriles has been carried out at room temperature using a highly reusable nanocrystalline ruthenium oxide pyrochlore Nafion composite catalyst (see figure).