Comparison of oxygen reduction reaction on Pt/C, Pt-Sn/C, Pt-Ni/C, and Pt-Sn-Ni/C catalysts prepared by Bönnemann method: A rotating ring disk electrode study

Electrochemically induced in vitro focal hypoxia in human neurons

Focalised hypoxia is widely prevalent in diseases such as stroke, cardiac arrest, and dementia. While in some cases hypoxia improves cellular functions, it mostly induces or exacerbates pathological changes. The lack of methodologies that can simulate focal acute hypoxia, in either animal or cell culture, impedes our understanding of the cellular consequences of hypoxia. To address this gap, an electrochemical localised oxygen scavenging system (eLOS), is reported, providing an innovative platform for spatiotemporal in vitro hypoxia modulation. The electrochemical system is modelled showing O₂ flux patterns and localised O₂ scavenging and hypoxia regions, as a function of distance from the electrode and surrounding flux barriers, allowing an effective focal hypoxia tool to be designed for in vitro cell culture study. O₂ concentration is reduced in an electrochemically defined targeted area from normoxia to hypoxia in about 6 min depending on the O₂-flux boundaries. As a result, a cell culture-well was designed, where localised O₂ scavenging could be induced. The impact of localised hypoxia was demonstrated on human neural progenitor cells (hNPCs) and it was shown that miniature focal hypoxic insults can be induced, that evoke time-dependent HIF-1α transcription factor accumulation. This transcription is "patterned" across the culture according to the electrochemically induced spatiotemporal hypoxia gradient. A basic lacunar infarct model was also developed through the application of eLOS in a purpose designed microfluidic device. Miniature focal hypoxic insults were induced in cellular processes of fully oxygenated cell bodies, such as the axons of human cortical neurons. The results demonstrate experimentally that localised axonal hypoxic stress can lead to significant increase of neuronal death, despite the neurons remaining at normoxia. This suggests that focal hypoxic insult to axons alone is sufficient to impact surrounding neurons and may provide an in vitro model to study the impact of microinfarcts occurring in the deep cerebral white matter, as well as providing a promising tool for wider understanding of acute hypoxic insults with potential to uncover its pathophysiology in multiple diseases.

Pt3Ni/C and Pt3Co/C cathodes as electrocatalysts for use in oxygen sensors and proton exchange membrane fuel cells

The composites Pt3Ni/C and Pt3Co/C are electrocatalysts for oxygen reduction reactions (ORRs). This study compares the electrocatalytic activity of these electrodes that are used to detect oxygen, and determines their suitability for use in proton exchange membrane fuel cells (PEMFCs). Chemical reduction is used to produce the Pt3Ni/C and Pt3Co/C electrocatalysts. The particle size, elemental composition and crystallinity of the intermetallic electrocatalysts are determined using transmission electron microscopy (TEM) and an energy-dispersive spectrometer (EDX). The ORR activity of the Pt3Ni/C and Pt3Co/C electrocatalysts is determined using cyclic voltammetry (CV), a polarization curve (PC) and a rotating disk electrode (RDE). The Pt3Ni/C electrode registers a greater current for the ORR as compared to the Pt3Co/C electrode. Both electrodes exhibit a linear relationship between response current and oxygen concentration in the detection range from 100 to 1000 ppm. The Pt3Ni/C electrode exhibits a significant sensitivity to oxygen up to 13.4 μA ppm−1 cm−2. A membrane electrode assembly (MEA) that is produced using Pt3Ni/C as a cathodic electrocatalyst in a single PEMFC generates a maximum power density of 1097 mW cm−2.

Amplified oxygen reduction signal at a Pt-Sn-modified TiO2 nanocomposite on an electrochemical aptasensor

In this work, a metallic composite with strong electrocatalytic property was designed by uniformly decorating Pt and Sn nanoparticles on the surface of TiO₂ nanorods (Pt-Sn@TiO₂). A detection scheme was then developed based on a dual signal amplification strategy involving the Pt-Sn@TiO₂ composite and exonuclease assisted target recycling. The Pt-Sn@TiO₂ composite exhibited an enhanced oxygen reduction current owing to the synergistic effect between Pt and Sn, as well as high exposure of Pt (111) crystal face. Initially, a Pt-Sn@TiO₂ modified glassy carbon electrode produced an amplified electrochemical signal for the reduction of dissolved oxygen in the analyte solution. Next, a DNA with a complementary sequence to a streptomycin aptamer (cDNA) was immobilised on the Pt-Sn@TiO₂ modified electrode, followed by the streptomycin aptamer that hybridised with cDNA. The corresponding oxygen reduction current was diminished by 51% attributable to the hindrance from the biomolecules. After a mixture of streptomycin and RecJ_f exonuclease was introduced, both the streptomycin-aptamer complex and the cDNA were cleaved from the electrode, making the Pt-Sn and Pt (111) surface available for oxygen reduction. RecJ_f would also release streptomycin from the streptomycin-aptamer complex, allowing it to complex again with aptamers on the electrode. This has then promoted a cyclic amplification of the oxygen reduction current by 85%, which is quantitatively related to streptomycin. Under optimal conditions, the aptasensor exhibited a linear range of 0.05-1500 nM and a limit of detection of 0.02±0.0045 nM streptomycin. The sensor was then used in the real-life sample detection of streptomycin to demonstrate its potential applications to bioanalysis.

A highly ordered honeycomb-like nickel(III/II) oxide-enhanced photocatalytic fuel cell for effective degradation of bisphenol A

The honeycomb-like nickel(III/II) oxide interpenetrated framework arrays labelled as H-NiO_x are used as cathode catalysts for the degradation of bisphenol A (BPA) in visible light-excited fuel cells. The nanoparticle close-packed NiO_x aggregates (C-NiO_x) and H-NiO_x are prepared by conventional electrodeposition (ED) and advanced oxidation-associated electrodeposition (AO-ED) strategies, carried out by multiple voltammetry controlled in the potential ranges of 0 to -1.3 V and 1.3 to -1.3 V (vs. SCE), respectively. Compared with C-NiO_x, the H-NiO_x frameworks with smaller charge transfer resistance and higher surface-confined redox-active centers exhibit larger cathode electrocatalytic activity for the photocatalytic degradation of BPA. The NaClO can act as a sacrificial agent to sustain the integrity and stability of H-NiO_x cathode. The H-NiO_x-assisted BPA degradation conditions are optimized by changing process variables. The BPA is degraded by 48.5% within 120 min in photocatalytic BPA (1.0 mmol L^-1, pH 13) fuel cell employing H-NiO_x cathode, CdS/TiO₂ photoanode and 0.2 mol L^-1 NaClO catholyte, and its degradation rate conforms to the first-order reaction kinetic model. The H-NiO_x can remarkably enhance the performances of the photocatalytic fuel cell, achieving a 4.1-fold or 15.2-fold increase in the short circuit current and maximum power density compared with that using bare cathode.

Assessing the electron transfer and oxygen mass transfer of the oxygen reduction reaction using a new electrode kinetic equation

A new kinetic equation describing the full-scale polarizations, provides a facile approach for assessing ORR performance, highlighting oxygen-mass transfer evaluation.

Low content Pt nanoparticles anchored on N-doped reduced graphene oxide with high and stable electrocatalytic activity for oxygen reduction reaction

A novel kind of Pt/N-rGO hybrid possessing of low content 5.31 wt.% Pt anchored on the surface of nitrogen doped reduced graphene oxide (N-rGO) evenly was prepared. The Pt has uniformed 2.8 nm diameter and exposed (111) crystal planes; meanwhile, the N works as the bridge between Pt and rGO with the Pt-N and N-C chemical bonds in Pt/N-rGO. The Pt/N-rGO material has a very high electrocatalytic activity in oxygen reduction reaction with the mass catalytic activity more than 1.5 times of the commercial Pt/C due to the synergistic catalytic effect of both N-doped carbon matrix and Pt nanoparticles. Moreover, the Pt/N-rGO exhibits an excellent stability with hardly loss (only 0.4%) after accelerated durability tests of 5000 cycles based on the stable Pt-N-C chemical bonds in Pt/N-rGO, which can prevent the detachment, dissolution, migration and aggregation of Pt nanoparticles on the matrix during the long-term cycling.

Facile Synthesis of Porous Dendritic Bimetallic Platinum-Nickel Nanocrystals as Efficient Catalysts for the Oxygen Reduction Reaction

Certain bimetallic nanocrystals (NCs) possess promising catalytic properties for electrochemical energy conversion. Herein, we report a facile method for the one-step synthesis of porous dendritic PtNi NCs in aqueous solution at room temperature that contrasts with the traditional multistep thermal decomposition approach. The dendritic PtNi NCs assembled by interconnected arms are efficient catalysts for the oxygen reduction reaction. This direct and efficient method is favorable for the up-scaled synthesis of active catalysts used in electrochemical applications.

The oxygen reduction reaction of ordered porous carbon-supported PtSn catalysts

Before and after ADT, the stabilization stems from electronic modification effect of synergistic Sn and OPC addition.

Carbon nanotubes-gold nanohybrid as potent electrocatalyst for oxygen reduction in alkaline media

A carbon nanotube-gold nanohybrid was used as catalyst for the reduction of molecular oxygen in acidic and alkaline media, the relevant cathode reaction in fuel cells. In alkaline medium, the nanohybrid exhibits excellent activity with a dominant 4e(-) reduction of O2 and low overpotential requirement compared to previously reported nano-gold materials. This property is linked to its capability to efficiently mediate HO2(-) dismutation.