Facile efficient earth abundant NiO/C composite electrocatalyst for the oxygen evolution reaction

Facile synthesis of nanostructured Ni/NiO/N-doped graphene electrocatalysts for enhanced oxygen evolution reaction

Electrocatalysts containing a Ni/NiO/N-doped graphene interface have been synthesised using the ligand-assisted chemical vapor deposition technique. NiO nanoparticles were used as the substrate to grow N-doped graphene by decomposing vapours of benzene and N-containing ligands. The method was demonstrated with two nitrogen-containing ligands, namely dipyrazino[2,3-f:2',3'-h]quinoxaline-2,3,6,7,10,11-hexacarbonitrile (L) and melamine (M). The structure and composition of the as-synthesized composites were characterized by XRD, Raman spectroscopy, SEM, TEM and XPS. The composite prepared using the ligand L had NiO sandwiched between Ni and N-doped graphene and showed an overpotential of 292 mV at 10 mA cm-2 and a Tafel slope of 45.41 mV dec-1 for the OER, which is comparable to the existing noble metal catalysts. The composite prepared using the ligand M had Ni encapsulated by N-doped graphene without NiO. It showed an overpotential of 390 mV at 10 mA cm-2 and a Tafel slope of 78.9 mV dec-1. The ligand-assisted CVD route demonstrates a facile route to control the microstructure of the electrocatalysts.

Construction of chitosan-supported nickel cobaltite composite for efficient electrochemical capacitor and water-splitting applications

The construction of highly efficient electrode material is of considerable interest, particularly for high capacitance and water-splitting applications. Herein, we present the preparation of a NiCo2O4-Chitosan (NC@Chit) nanocomposite using a simple hydrothermal technique designed for applications in high capacitance and water-splitting. The structure/composition of the NC@Chit composite was characterized using different analytical methods, containing electron microscope (SEM and TEM), and powder X-ray diffraction (XRD). When configured as an anode material, the NC@Chit displayed a high capacitance of 234 and 345 F g-1 (@1Ag-1 for GC/NC and NC@Chit, respectively) in an alkaline electrolyte. The direct use of the catalyst in electrocatalytic water-splitting i.e., HER and OER achieved an overpotential of 240 mV and 310 mV at a current density of 10 mA cm-2, respectively. The obtained Tafel slopes for OER and HER were 62 and 71 mV dec-1, respectively whereas the stability and durability of the fabricated electrodes were assessed through prolonged chronoamperometry measurement at constant for 10 h. The electrochemical water splitting was studied for modified nickel cobaltite surface using an impedance tool, and the charge transfer resistances were utilized to estimate the electrode activity.

A vertically paired electrode for redox cycling and its application to immunoassays

An electrochemical immunoassay based on the redox cycling method was presented using vertically paired electrodes (VPEs), which were fabricated using poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as an electrode material and parylene-C as a dielectric layer. For the application to immunoassays, different electrochemical properties of PEDOT:PSS were analyzed for the redox reaction of 3,3',5,5'-tetramethylbenzidine (TMB, the chromogenic substrate for enzyme-immunoassays) at different pH conditions, including the conductivity (σ), electron transfer rate constant (k_app), and double-layer capacitance (C_dl). The influencing factors on the sensitivity of redox cycling based on VPE based on PEDOT:PSS were analyzed for the redox reaction of TMB, such as the electrode gap and number of electrode pairs. Computer simulation was also performed for the redox cycling results based on VPEs, which had limitations in fabrication, such as VPEs with an electrode gap of less than 100 nm and more than five electrode pairs. Finally, the redox cycling based on VPE was applied to the medical diagnosis of human hepatitis-C virus (hHCV) using a commercial ELISA kit. The sensitivity of the redox cycling method for the medical diagnosis of hHCV was compared with conventional assay methods, such as TMB-based chromogenic detection, luminol-based chemiluminescence assay, and a rapid test kit (lateral flow immunoassay).

Carbonaceous Oxygen Evolution Reaction Catalysts: From Defect and Doping-Induced Activity over Hybrid Compounds to Ordered Framework Structures

Oxygen evolution reaction (OER) is expected to be of great importance for the future energy conversion and storage in form of hydrogen by water electrolysis. Besides the traditional noble-metal or transition metal oxide-based catalysts, carbonaceous electrocatalysts are of great interest due to their huge structural and compositional variety and unrestricted abundance. This review provides a summary of recent advances in the field of carbon-based OER catalysts ranging from "pure" or unintentionally doped carbon allotropes over heteroatom-doped carbonaceous materials and carbon/transition metal compounds to metal oxide composites where the role of carbon is mainly assigned to be a conductive support. Furthermore, the review discusses the recent developments in the field of ordered carbon framework structures (metal organic framework and covalent organic framework structures) that potentially allow a rational design of heteroatom-doped 3D porous structures with defined composition and spatial arrangement of doping atoms to deepen the understanding on the OER mechanism on carbonaceous structures in the future. Besides introducing the structural and compositional origin of electrochemical activity, the review discusses the mechanism of the catalytic activity of carbonaceous materials, their stability under OER conditions, and potential synergistic effects in combination with metal (or metal oxide) co-catalysts.

Phyto-inspired and scalable approach for the synthesis of PdO-2Mn2O3: a nano-material for application in water splitting electro-catalysis

A modified co-precipitation method has been used for the synthesis of a PdO-2Mn₂O₃ nanocomposite as an efficient electrode material for the electro-catalytic oxygen evolution (OER) and hydrogen evolution reaction (HER). Palladium acetate and manganese acetate in molar ratio 1 : 4 were dissolved in water, and 10 ml of an aqueous solution of phyto-compounds was slowly added until completion of precipitation. The filtered and dried precipitates were then calcined at 450 °C to obtain a blackish brown colored mixture of PdO-2Mn₂O₃ nanocomposite. These particles were analyzed by ultra violet visible spectrophotometry (UV-vis), infrared spectroscopy (FTIR), powder X-ray diffractometry (XRD), scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS) for crystallinity, optical properties, and compositional and morphological makeup. Using Tauc's plot, the direct band gap (3.18 eV) was calculated from the absorption spectra. The average crystallite sizes, as calculated from the XRD, were found to be 15 and 14.55 nm for PdO and Mn₂O₃, respectively. A slurry of the phyto-fabricated PdO-2Mn₂O₃ powder was deposited on Ni-foam and tested for electro-catalytic water splitting studies in 1 M KOH solution. The electrode showed excellent OER and HER performance with low over-potential (0.35 V and 121 mV) and Tafel slopes of 115 mV dec^-1 and 219 mV dec^-1, respectively. The outcomes obtained from this study provide a direction for the fabrication of a cost-effective mixed metal oxide based electro-catalyst via an environmentally benign synthesis approach for the generation of clean energy.

Excellent Oxygen Evolution Reaction of Activated Carbon-Anchored NiO Nanotablets Prepared by Green Routes

A sustainable and efficient electrocatalyst for the oxygen evolution reaction (OER) is vital to realize green and clean hydrogen production technology. Herein, we synthesized the nanocomposites of activated carbon-anchored nickel oxide (AC-NiO) via fully green routes, and characterized their excellent OER performances. The AC-NiO nanocomposites were prepared by the facile sonication method using sonochemically prepared NiO nanoparticles and biomass-derived AC nanosponges. The nanocomposites exhibited an aggregated structure of the AC-NiO nanotablets with an average size of 40 nm. When using the nanotablets as an OER catalyst in 1 M KOH, the sample displayed superb electrocatalytic performances, i.e., a substantially low value of overpotential (320 mV at 10 mA/cm2), a significantly small Tafel slope (49 mV/dec), and a good OER stability (4% decrease of overpotential after 10 h). These outstanding OER characteristics are considered as attributing to the synergetic effects from both the ample surface area of the electrochemically active NiO nanoparticles and the high electrical conductivity of the AC nanosponges. The results pronounce that the fully ecofriendly synthesized AC-NiO nanotablets can play a splendid role as high-performance electrocatalysts for future green energy technology.

Cobalt oxide nanoparticle-decorated reduced graphene oxide (Co3O4–rGO): active and sustainable nanoelectrodes for water oxidation reaction

Herein, cobalt oxide (Co₃O₄)-decorated reduced graphene oxide (rGO)-based nanoelectrodes were fabricated by the chemical reduction method for electrocatalytic water oxidation reactions.