MOF-derived S-doped NiCo2O4 hollow cubic nanocage for highly efficient electrocatalytic oxygen evolution.

Inducing the surface reconstruction of spinels is critical for improving the electrocatalytic oxygen evolution reaction (OER) activity. Herein, S-doped NiCo2O4 hollow cubic nanocage was synthesized by anion etching Metal-Organic Frameworks (MOFs) template and air annealing strategies. The hollow structure possesses a large specific surface area and pore size, facilitating active site exposure and mass transport. S2- doping regulates the electronic structure, reducing the oxidation potential of Ni sites during the OER process, thus promoting the surface reconstruction into γ-NiOOH active species. Meanwhile, S2- doping enhances conductivity, accelerating interfacial charge transfer. As a result, S-NiCo2O4-6 exhibits superior OER activity (262 mV overpotential @ 10 mA cm-2) and stability in 1.0 M KOH solution. Furthermore, 20 % Pt/C‖S-NiCo2O4-6 only needs 1.832 V to achieve 50 mA (the electrochemical active area is 4 cm2) in a homemade anion exchange membrane (AEM) electrolyzer. This work proposes a novel approach for preparing efficient anion-doped spinel-based OER electrocatalysts.

CoMoO4-CoP/NC heterostructure anchored on hollow polyhedral N-doped carbon skeleton for efficient water splitting.

We report the synthesis and electrocatalytic properties of a CoMoO4-CoP heterostructure anchored on a hollow polyhedral N-doped carbon skeleton (CoMoO4-CoP/NC) for water-splitting applications. The preparation involved the anion exchange of MoO42- to the organic ligand of ZIF-67, the self-hydrolysis of MoO42-, and NaH2PO2 phosphating annealing. CoMoO4 was found to enhance thermal stability and prevent active site agglomeration during annealing, while the hollow structure of CoMoO4-CoP/NC provided a large specific surface area and high porosity that facilitated mass transport and charge transfer. The interfacial electron transfer from Co to Mo and P sites promoted the generation of electron-deficient Co sites and electron-enriched P sites, which accelerated water dissociation. CoMoO4-CoP/NC exhibited excellent electrocatalytic activity for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in 1.0 M KOH solution, with overpotentials of 122 mV and 280 mV at 10 mA cm-2, respectively. The CoMoO4-CoP/NC‖CoMoO4-CoP/NC two-electrode system only required an overall water splitting (OWS) cell voltage of 1.62 V to achieve 10 mA cm-2 in an alkaline electrolytic cell. In addition, the material showed comparable activity to 20% Pt/C‖RuO2 in a pure water home-made membrane electrode device, demonstrating potential for practical applications in proton exchange membrane (PEM) electrolyzers. Our results suggest that CoMoO4-CoP/NC is a promising electrocatalyst for efficient and cost-effective water splitting.

Enhancing electro-reduction of nitrite to ammonia by loading Co3O4 on CuO to construct elecrocatalytic dual-sites.

Improving the performance of CuO in electrocatalytic nitrite reduction to ammonia (NIRA) is the priority for designing efficient NIRA electrocatalysts. The electrocatalytic activity of CuO was enhanced by growing Co3O4 nanospheres on it. By comparing Co3O4@CuO with the mechanically mixed CuO and Co3O4 on a rotating ring-disk electrode, we discovered that the enhancement was attributed to a dual-site catalytic pathway.

Surface charge modulation enhanced high stability of gold oxidation intermediates for electrochemical glucose sensors.

Rapid and accurate blood glucose detection is significant for diagnosing and treating diabetes. Herein, ultra-low-content gold nanoparticles were loaded on different metal foams and applied to electrochemical enzyme-free glucose sensors via simple displacement reactions. The structures and properties of the produced catalysts were determined by various characterization methods. The performance of the glucose sensor was examined in relation to the interactions between three different metal substrates and gold. The one with the best performance is the sample of gold nanoparticles grown on copper foam (Au300 Cu Foam). It has the advantage of a porous three-dimensional network, a large electroactive surface area, and the high catalytic activity of gold. The combination of Cu and Au increased the valence state of Au, thus favoring the catalytic activity for glucose oxidation. Cyclic voltammetry and chronoamperometry measurements revealed that Au is responsible for the electrocatalytic oxidation of glucose. The sensitivity of Au300 Cu Foam was found to be 10 839 µA mM-1 cm-2 in the linear range of 0.00596-0.0566 mM, with a detection limit (LOD) of 0.223 µM, and 2-3 s response time at 0.4 V vs. Ag/AgCl. The Au300 Cu Foam glucose sensor also offered outstanding stability and anti-interference performance. The prepared Au300 Cu Foam electrode was also successfully applied to detect different levels of glucose in human body fluids, such as saliva. These characteristics make Au300 Cu Foam promising for non-invasive glucose detection.

Flexible Single-Electrode Triboelectric Nanogenerator and Body Moving Sensor Based on Porous Na2CO3/Polydimethylsiloxane Film.

Triboelectric nanogenerators (TENGs) converting mechanical energy into electrical energy have received much attention because of their huge potential applications for supplying power to electronic devices. Improving the performance of TENGs has become a research hot point because of their output limited current. In this paper, we propose a flexible single-electrode triboelectric nanogenerator based on porous Na2CO3/polydimethylsiloxane (PDMS) structure to enhance the triboelectric performance for nanogenerators. To compare their output performance, NaCl and sugar are normally used as sacrificial template for triboelectric nanogenerator. As an experimental result, the nanogenerator based on porous Na2CO3/PDMS structure obtains the open-circuit voltage of 125 V and maximum output current of 100 µA, which are higher than that generated by NaCl/PDMS and sugar/PDMS TENGs. And the generated electric energy of Na2CO3/PDMS TENG could instantaneously power 42 commercial light-emitting diodes without any energy storage devices. This developed porous Na2CO3/PDMS TENG could open a new application field for self-powered personal electronics because of its flexibility, simple manufacturing process, and the ability to harvest mechanical energy from human motions.

A flexible triboelectric-piezoelectric hybrid nanogenerator based on P(VDF-TrFE) nanofibers and PDMS/MWCNT for wearable devices.

This paper studied and realized a flexible nanogenerator based on P(VDF-TrFE) nanofibers and PDMS/MWCNT thin composite membrane, which worked under triboelectric and piezoelectric hybrid mechanisms. The P(VDF-TrFE) nanofibers as a piezoelectric functional layer and a triboelectric friction layer are formed by electrospinning process. In order to improve the performance of triboelectric nanogenerator, the multiwall carbon nanotubes (MWCNT) is doped into PDMS patterned films as the other flexible friction layer to increase the initial capacitance. The flexible nanogenerator is fabricated by low cost MEMS processes. Its output performance is characterized in detail and structural optimization is performed. The device's output peak-peak voltage, power and power density under triboelectric mechanism are 25 V, 98.56 µW and 1.98 mW/cm3 under the pressure force of 5 N, respectively. The output peak-peak voltage, power and power density under piezoelectric working principle are 2.5 V, 9.74 µW, and 0.689 mW/cm3 under the same condition, respectively. We believe that the proposed flexible, biocompatible, lightweight, low cost nanogenerator will supply effective power energy sustainably for wearable devices in practical applications.

A flexible and biocompatible triboelectric nanogenerator with tunable internal resistance for powering wearable devices.

Recently, triboelectric energy nanogenerators (TENGs) have been paid the most attention by many researchers to convert mechanical energy into electrical energy. TENGs usually have a simple structure and a high output voltage. However, their high internal resistance results in low output power. In this work, we propose a flexible triboelectric energy nanogenerator with the double-side tribological layers of polydimethlysiloxane (PDMS) and PDMS/multiwall carbon nanotube (MWCNT). MWCNTs with different concentrations have been doped into PDMS to tune the internal resistance of triboelectric nanogenerator and optimize its output power. The dimension of the fabricated prototype is ~3.6 cm(3). Three-axial force sensor is used to monitor the applied vertical forces on the device under vertical contact-separation working mode. The Prototype with 10 wt% MWCNT (Prototype I) produces higher output voltage than one with 2 wt% MWCNT (Prototype II) due to its higher dielectric parameter measured by LRC impedance analyzer. The triboelectric output voltages of Prototype I and Prototype II are 30 V and 25 V under the vertical force of 3.0 N, respectively. Their maximum triboelectric output powers are ~130 µW at 6 MΩ and ~120 µW at 8.6 MΩ under vertical forces, respectively.