Enhanced Oxygen Evolution via Electrochemical Water Oxidation using Conducting Polymer and Nanoparticle Composites

Nano-Co₃ O₄ was used for electrocatalytic water oxidation due to its promising features of better performance and low cost. An enhanced electrochemical water oxidation performance of the nanoparticles can be achieved by mixing them with other types of highly conductive nano/micro-structured materials. Conductive polymers would be one of the candidates to achieve this goal. Here, we report our recently developed nano-Co₃ O₄ and polypyrrole composites for enhanced electrochemical water oxidation. We chose polypyrrole as a support of nano-Co₃ O₄ to obtain highly active sites of nano-Co₃ O₄ with high conductivity. Morphological and chemical characterization of the prepared materials were performed using scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS). After immobilizing them individually on fluorine doped tin oxide (FTO) substrate, their electrocatalytic properties toward water oxidation were investigated. The optimum composite materials showed significantly higher electrocatalytic properties compared to that of pure nano-Co₃ O₄ and polypyrrole. Electrochemical impedance studies indicated that the composite materials possess significantly less electron transfer resistance toward water oxidation reaction compared to that of only polypyrrole or nano-Co₃ O₄ , while the higher double-layer capacitance and polarization resistance values obtained from fitting of the impedance data represent the faster electrode kinetics in the composite electrocatalyst. Due to the synergetic effect, the optimum nano-Co₃ O₄ and polypyrrole composites could be represent a novel and promising material for water oxidation.

Ultrasensitive SERS detection of rhodamine 6G and p-nitrophenol based on electrochemically roughened nano-Au film

Quantitative analysis of organic pollutants in environmental water is an important issue for ecological environment and human health. In this paper, the quantitative analysis of rhodamine 6G (R6G) and p-nitrophenol (PNP) is performed by the surface enhanced Raman scattering (SERS) technology. The enhancement of Raman signals is achieved on the surface of an electrochemically roughened nano-Au film. The SERS performance depends on the microstructure of roughened nano-Au films, which is affected by the thickness of Au films and electrochemical roughening parameters. The structure-dependence of SERS performance is validated by finite element simulation of local electromagnetic field distribution. An obvious SERS effect of R6G with an enhancement factor of 10⁸ is obtained on the roughened nano-Au film. A sensitive SERS detection of R6G with a linear range of 10^-9-10^-5 M and a detection limit of 10^-11 M is realized. Moreover, a wide linear range of 10^-9-10^-3 M is obtained for the detection of PNP. The roughened nano-Au film is an effective substrate for the SERS detection of organic pollutants with high reproducibility and good stability. Therefore, the electrochemical technology in this study is expected to be a very promising method for the fabrication of high-performance SERS substrate.

Mixed-Ligand-Architected 2D Co(II)-MOF Expressing a Novel Topology for an Efficient Photoanode for Water Oxidation Using Visible Light

The structural diversity of Co(II) metal centers is known to influence their physicochemical properties. A novel two-dimensional (2D) Co(II)-MOF {[Co₅(HL)₄(dpp)₂(H₂O)₂(μ-OH)₂]·21H₂O} n has been designed and synthesized by adopting a mixed-ligand strategy, using 1,3-di(4-pyridyl)propane (dpp) colinker with a flexible spacer H₃L (H₃L: 5-(2 carboxybenzyloxy)isophthalic acid). Co(II)-MOF features a 2D network, which is further interpenetrated among the equivalent sets and therefore results in a 3D supramolecular network. Topologically, the entire network can be viewed as a (3,4,8)-connected three-nodal net with the extended point symbol of {4.5.7}4{4¹².5².7¹⁰.9⁴}{5².8.9².10}2, duly assigned to the novel topological type smm2. The functional utility of Co(II)-MOF is demonstrated by employing it toward oxygen evolution reaction (OER) in a photoelectrochemical cell, exhibiting appreciable photocurrents of up to 5.89 mA/cm² when used as an anode in a photoelectrochemical cell, while also displaying encouraging electrocatalytic currents of 9.32 mA/cm² (at 2.01 V vs RHE) for the OER. Moreover, detailed electrochemical impedance spectroscopy studies confirm enhanced charge-transfer kinetics and improved conductivity under illumination with minimal effect of interfacial phenomena. This work provides a reference for the expanding field of research into applications of MOF materials and establishes MOF materials as favorable candidates for sustainable and efficient design of electrodes for water splitting.