Electrocatalysis: present and future

Advances in non-enzymatic glucose sensors based on metal oxides

This review summarizes the advances in non-enzymatic glucose sensors based on different metal oxides (ZnO, CuO/Cu₂O, NiO,etc.) and their composites.

An electrokinetic-combined electrochemical study of the glucose electro-oxidation reaction: effect of gold surface energy

Electrokinetic analysis demonstrates the effect of glucose adsorption on gold surfaces in the glucose electro-oxidation mechanism.

Metal-organic frameworks derived CoxFe1-xP nanocubes for electrochemical hydrogen evolution

Designing and developing active, cost-effective and stable electrocatalysts for hydrogen evolution reaction (HER) are still an ongoing challenge. Herein, we report the synthesis of binary transition metal phosphide (CoxFe1-xP) nanocubes with different Co and Fe ratios through a phosphidation process using metal-organic frameworks (MOFs) as templates. MOF templates contribute well-defined nanocube architectural features after phosphidation, while a suitable phosphidation temperature could allow formation of a crystal structure and maintain the well-defined structure. The incorporation of a binary transition metal results in redistribution of the valence electrons in CoxFe1-xP. The changes imply anionic states of the P and Fe atoms, which act as active sites and thus have stronger electron-donating ability. When CoxFe1-xP nanocubes are employed as electrocatalysts, these characteristic features facilitate the performance of HER. Remarkably, Co0.59Fe0.41P nanocubes prepared at 450 °C afford a current density of 10 mA cm(-2) at a low overpotential of 72 mV in acidic conditions and 92 mV in alkaline conditions. Co0.59Fe0.41P nanocubes also exhibit a small Tafel slope of 52 mV decade(-1) in acidic conditions and 72 mV decade(-1) in alkaline conditions. Moreover, Co0.59Fe0.41P nanocubes show good stability in both acidic and alkaline conditions. Our method produces the highly active HER catalyst based on binary transition metal MOF templates, providing a new avenue for designing excellent electrocatalysts.

Fabrication of a microneedle/CNT hierarchical micro/nano surface electrochemical sensor and its in-vitro glucose sensing characterization

We report fabrication of a microneedle-based three-electrode integrated electrochemical sensor and in-vitro characterization of this sensor for glucose sensing applications. A piece of silicon was sequentially dry and wet etched to form a 15 × 15 array of tall (approximately 380 μm) sharp silicon microneedles. Iron catalyst was deposited through a SU-8 shadow mask to form the working electrode and counter electrode. A multi-walled carbon nanotube forest was grown directly on the silicon microneedle array and platinum nano-particles were electrodeposited. Silver was deposited on the Si microneedle array through another shadow mask and chlorinated to form a Ag/AgCl reference electrode. The 3-electrode electrochemical sensor was tested for various glucose concentrations in the range of 3∼20 mM in 0.01 M phosphate buffered saline (PBS) solution. The sensor's amperometric response to the glucose concentration is linear and its sensitivity was found to be 17.73 ± 3 μA/mM-cm². This microneedle-based sensor has a potential to be used for painless diabetes testing applications.

Large amplitude Fourier transformed AC voltammetric investigation of the active state electrochemistry of a copper/aqueous base interface and implications for electrocatalysis

The higher harmonic components available from large-amplitude Fourier-transformed alternating current (FT-ac) voltammetry enable the surface active state of a copper electrode in basic media to be probed in much more detail than possible with previously used dc methods. In particular, the absence of capacitance background current allows low-level Faradaic current contributions of fast electron-transfer processes to be detected; these are usually completely undetectable under conditions of dc cyclic voltammetry. Under high harmonic FT-ac voltammetric conditions, copper electrodes exhibit well-defined and reversible premonolayer oxidation responses at potentials within the double layer region in basic 1.0 M NaOH media. This process is attributed to oxidation of copper adatoms (Cu*) of low bulk metal lattice coordination numbers to surface-bonded, reactive hydrated oxide species. Of further interest is the observation that cathodic polarization in 1.0 M NaOH significantly enhances the current detected in each of the fundamental to sixth FT-ac harmonic components in the Cu*/Cu hydrous oxide electron-transfer process which enables the underlying electron transfer processes in the higher harmonics to be studied under conditions where the dc capacitance response is suppressed; the results support the incipient hydrous oxide adatom mediator (IHOAM) model of electrocatalysis. The underlying quasi-reversible interfacial Cu*/Cu hydrous oxide process present under these conditions is shown to mediate the reduction of nitrate at a copper electrode, while the mediator for the hydrazine oxidation reaction appears to involve a different mediator or active state redox couple. Use of FT-ac voltammetry offers prospects for new insights into the nature of active sites and electrocatalysis at the electrode/solution interface of Group 11 metals in aqueous media.