An enzyme-free electrochemical biosensor based on target-catalytic hairpin assembly and Pd@UiO-66 for the ultrasensitive detection of microRNA-21
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Abstract As well known, heteroatom doped carbon material served as metal‐free electrocatalyst for hydrogen evolution (HER) and oxygen reduction reactions (ORR) particularly relies on the heteroatom doping level. Here, we report a 3D porous nitrogen doped carbon (PNC) electrocatalyst with superior HER and ORR electrocatalytic activities derived from the calcination of the discarded cigarette butt and dicyandiamide possessing a high nitrogen content (20 at%). PNC electrocatalyst only demands 143 mV versus RHE to achieve 10 mA cm −2 ascribed to the high nitrogen percentile in PNC electrocatalyst favorable for constructing successive active centers contributing to efficiently catalyzing HER. Ignorable degradation in HER activity observed after 10000 potential cycles as well as undetectable decay in HER performance recorded after 12 h operation indicate high stability of PNC electrocatalyst. Meanwhile, half‐wave potential of PNC electrocatalyst reaches 0.81 V versus RHE in 1 M KOH electrolyte. Additionally, stable ORR activity attained after 1000 potential cycles is indicative of high stability. A comparably high zinc‐air battery performance with maximum power density of 66 mW cm −2 is achieved by PNC electrocatalyst. This study highlights the importance of nitrogen doping level in metal‐free electrocatalyst for boosting HER and ORR activities.
Heteroatom
Reversible hydrogen electrode
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The principle,character and classification of enzyme biosensor are introduced.The ways to achieve electric signal of the first generation biosensor,the superiorities of the second generation biosensor with medium and the methods and materials to fixate enzyme of the third generation enzyme biosensor are expounded.The present conditions of the third generation enzyme biosensor are commented on.Finally,the progressive directions of biosensor have also been prospected.
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Carbon fibers
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Electrocatalysis as a catalytic process involving oxidation or reduction through the direct transfer of electrons is of key importance subject in various fields of chemistry and associated sciences. Heterogeneous electrocatalysis is especially important to the development of water oxidation and fuel cells catalysts. This paper presents the brief description of the electrocatalysis and the mechanism of electrochemical reactions. Different factors and their influence on electrocatalytic activity, have been discussed. Role of nanoparticles in electrocatalysis received a particular emphasis. Long-term tasks of electrocatalysis were also definied.
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Overpotential
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Metal-organic framework (MOF) based composite materials have attracted significant research interest in the electrocatalytic field. In this study, a carbonized polypyrrole coated MOF composite electrocatalyst ([email protected]) is developed, which is a nitrogen-modified MOF-based carbon used as non-precious oxygen reduction reaction (ORR) electrocatalyst. Physical characterizations prove that the [email protected] electrocatalyst has high nitrogen doping (2.53 at.%) and effective graphite and pyridinium nitrogen doping (86.6%). When compared with commercial Pt/C, as-obtained [email protected] electrocatalyst shows good ORR performance (∆E1/2 = −22 mV) with good stability (87.8%) and methanol tolerance. All results indicate that MOF-based [email protected] electrocatalyst is an effective and promising electrocatalyst for ORR.
Carbon fibers
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La 0.6 Ca 0.4 CoO 3 perovskite electrocatalyst had been synthesized by organic acid-aided method. The impact of the cal-cining conditions on the electrocatalyst preparation was studied by XRD, TEM and optimal results were given. The perfor-mance of bifunctional oxygen electrode electrocatalyst was evaluated preliminarily by galvanostatic polarization curve method. The results show that the electrocatalyst synthesized at 700 ℃for 2h has the characteristics of single phase, single crystal and smaller grain size, so the condition is optimal for preparing the electrocatalyst. The electrocatalyst made under that condition has better bifunctional oxygen electrode electrocatalytic activity and stability, which is promising as bifunctional oxygen elec-trode electrocatalyst for the MH-Air secondary battery application.
Clark electrode
Oxygen evolution
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Chemisorption
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