ABSTRACT
Despite the enormous attention paid to cobalt oxide materials as efficient water splitting electrocatalysts, a deep understanding of their activity discrepancy is still elusive. In this work, we showed that stabilization of the internally generated oxygen evolution reaction (OER) active phase (oxyhydroxide) is crucial for ZnCo2O4 electrocatalysts. A systematic evaluation of the bulk and nanostructured ZnCo2O4 system concomitant with nanostructured Co3O4 showed that leaching of Zn is the driving force behind the near-surface transformation to the oxyhydroxide phase. The relative contribution to this near-surface reconstruction was found to be surface-sensitive. The electrochemical observations combined with Raman and impedance spectroscopy revealed that the good catalytic activity could be attributed to the formation of the cobalt oxyhydroxide phase, which was created by the dissolution of Zn from the nanostructured surface. Moreover, this study sheds light on previous contradicting postulates regarding the discrepancy of the OER activity of ZnCo2O4. Our finding regarding the formation of the OER active phase in spinel Zn-Co oxide will motivate researchers to focus more on the near-surface reconstruction behavior of cobalt-based oxide electrocatalysts in the future.
ABSTRACT
A flexible and disposable strip sensor for non-enzymatic glucose detection is demonstrated in this work. The strips are prepared by using chemical modification processes followed by a simple electroless deposition of copper. Essentially, polyester overhead projector (OHP) transparent films are modified with a monolayer of 3-aminopropyltrimethoxysilane (APTMS) and polyaniline (PANI) conducting polymer. Later, nanostructured copper is deposited onto this modified film. Scanning electron microscope (SEM) and X-ray diffraction (XRD) studies are used for the structural, morphological and crystallinity characterization of the modified films. Electrochemical techniques, namely cyclic voltammetry (CV) and chronoamperometry (CA), are employed for the non-enzymatic detection of glucose. These studies clearly reveal the formation of homogeneous, close-packed spherical Cu particles converged into uniform film that exhibits a good catalytic activity towards the oxidation of glucose. The Cu/PANI/APTMS/OHP sensor displays a remarkable enhancement in the oxidation current density, a very high sensitivity value of 2.8456 mA cm(-2) per mM, and a linear concentration range from 100 µM to 6.5 mM associated with glucose detection. Detection limit is estimated to be 5 µM and the response time of the sensor is determined to be less than 5 s. For comparison, similar studies are performed without PANI, namely Cu/APTMS/OHP films for glucose detection. In this case, a sensitivity value of 2.4457 mA cm(-2) per mM and a linear concentration range of 100 µM-3 mM are estimated. The higher performance characteristics observed in the case of Cu/PANI/APTMS/OHP are attributed to the synergistic effects of the conducting polymer acting as an electron facilitator and the nanostructured Cu films. These disposable, flexible and low-cost strip sensors have also been applied to the detection of glucose in clinical blood serum samples and the results obtained agree very well with the actual glucose level.
