Spongelike Nanoporous Pd and Pd/Au Structures: Facile Synthesis and Enhanced Electrocatalytic Activity

This paper reports the facile synthesis and characterization of spongelike nanoporous Pd (snPd) and Pd/Au (snPd/Au) prepared by a tailored galvanic replacement reaction (GRR). Initially, a large amount of Co particles as sacrificial templates was electrodeposited onto the glassy carbon surface using a cyclic voltammetric method. This is the key step to the subsequent fabrication of the snPd/Au (or snPd) architectures by a surface replacement reaction. Using Co films as sacrificial templates, snPd/Au catalysts were prepared through a two-step GRR technique. In the first step, the Pd metal precursor (at different concentrations), K₂PdCl₄, reacted spontaneously to the formed Co frames through the GRR, resulting in a snPd series. snPd/Au was then prepared via the second GRR between snPd (prepared with 27.5 mM Pd precursor) and Au precursor (10 mM HAuCl₄). The morphology and surface area of the prepared snPd series and snPd/Au were characterized using spectroscopic and electrochemical methods. Rotating disk electrode (RDE) experiments for oxygen reduction in 0.1 M NaOH showed that the snPd/Au has higher catalytic activity than snPd and the commercial Pd-20/C and Pt-20/C catalysts. Rotating ring-disk electrode (RRDE) experiments reconfirmed that four electrons were involved in the electrocatalytic reduction of oxygen at the snPd/Au. Furthermore, RDE voltammetry for the H₂O₂ oxidation/reduction was used to monitor the catalytic activity of snPd/Au. The amperometric <i>i</i>–<i>t</i> curves of the snPd/Au catalyst for a H₂O₂ electrochemical reaction revealed the possibility of applications as a H₂O₂ oxidation/reduction sensor with high sensitivity (0.98 mA mM^–1 cm^–2 (<i>r</i> = 0.9997) for H₂O₂ oxidation and −0.95 mA mM^–1 cm^–2 (<i>r</i> = 0.9997) for H₂O₂ reduction), low detection limit (1.0 μM), and a rapid response (<∼1.5 s)

Ternary Composite of Polyaniline Graphene and TiO₂ as a Bifunctional Catalyst to Enhance the Performance of Both the Bioanode and Cathode of a Microbial Fuel Cell

Microbial fuel cells (MFCs) are a potential sustainable energy resource by converting organic pollutants in wastewater to clean energy. The performance of MFCs is influenced directly by the electrode material. In this study, a ternary PANI-TiO₂-GN nanocomposite was used successfully to improve the performance of both the cathode and anode MFC. The PANI-TiO₂-GN catalyst exhibited better oxygen reduction reaction activity in the cathode, particularly as a superior catalyst for improved extracellular electron transfer to the anode. This behavior was attributed to the good electronic conductivity, long-term stability, and durability of the composite. The immobilization of bacteria and catalyst matrix in the anode facilitated more extracellular electron transfer (EET) to the anode, which further improved the performance of the MFCs. The application of PANI-TiO₂-GN as a bifunctional catalyst in both the cathode and anode helped decrease the cost of MFCs, making it more practical

Hierarchically Driven IrO₂ Nanowire Electrocatalysts for Direct Sensing of Biomolecules

Applying nanoscale device fabrications toward biomolecules, ultra sensitive, selective, robust, and reliable chemical or biological microsensors have been one of the most fascinating research directions in our life science. Here we introduce hierarchically driven iridium dioxide (IrO₂) nanowires directly on a platinum (Pt) microwire, which allows a simple fabrication of the amperometric sensor and shows a favorable electronic property desired for sensing of hydrogen peroxide (H₂O₂) and dihydronicotinamide adenine dinucleotide (NADH) without the aid of enzymes. This rational engineering of a nanoscale architecture based on the direct formation of the hierarchical 1-dimensional (1-D) nanostructures on an electrode can offer a useful platform for high-performance electrochemical biosensors, enabling the efficient, ultrasensitive detection of biologically important molecules

Growth of Highly Single Crystalline IrO₂ Nanowires and Their Electrochemical Applications

We present the facile growth of highly single crystalline iridium dioxide (IrO₂) nanowires on SiO₂/Si and Au substrates via a simple vapor phase transport process under atmospheric pressure without any catalyst. Particularly, high-density needle-like IrO₂ nanowires were readily obtained on a single Au microwire, suggesting that the melted surface layer of Au might effectively enhance the nucleation of gaseous IrO₃ precursors at the growth temperature. In addition, all the electrochemical observations of the directly grown IrO₂ nanowires on a single Au microwire support favorable electron-transfer kinetics of [Fe­(CN₆)]^4–/3– as well as Ru­(NH₃)₆^3+/2+ at the highly oriented crystalline IrO₂ nanowire surface. Furthermore, stable pH response is shown, revealing potential for use as a miniaturized pH sensor, confirmed by the calibration curve exhibiting super-Nernstian behavior with a slope of 71.6 mV pH^–1