Structure and activity of nanozymes: Inspirations for de novo design of nanozymes

Alkaline anion-exchange membrane (AAEM) fuel cells have attracted significant interest in the past decade, thanks to the recent developments in hydroxide-anion conductive membranes. In this article, we compare the performance of current state of the art AAEM fuel cells to proton-exchange membrane (PEM) fuel cells and elucidate the sources of various overpotentials. While the continued development of highly conductive and thermally stable anion-exchange membranes is unambiguously a principal requirement, we attempt to put the focus on the challenges in electrocatalysis and interfacial charge transfer at an alkaline electrode/electrolyte interface. Specifically, a critical analysis presented here details the (i) fundamental causes for higher overpotential in hydrogen oxidation reaction, (ii) mechanistic aspects of oxygen reduction reaction, (iii) carbonate anion poisoning, (iv) unique challenges arising from the specific adsorption of alkaline ionomer cation-exchange head groups on electrocatalysts surfaces, and (v) the potential of alternative small molecule fuel oxidation. This review and analysis encompasses both the precious and nonprecious group metal based electrocatalysts from the perspective of various interfacial charge-transfer phenomena and reaction mechanisms. Finally, a research roadmap for further improvement in AAEM fuel cell performance is delineated here within the purview of electrocatalysis and interfacial charge transfer.

Alkaline Anion-Exchange Membrane Fuel Cells: Challenges in Electrocatalysis and Interfacial Charge Transfer.

The development of efficient heterogeneous Fenton catalysts is mainly by “trial-and-error” concept and the factor determining H2O2 activation remains elusive. In this work, we demonstrate that suitable facet exposure to elongate O–O bond in H2O2 is the key parameter determining the Fenton catalyst’s activity. CuFeO2 nanocubes and nanoplates with different surface facets of {110} and {012} are used to compare the effect of exposed facets on Fenton activity. The results indicate that ofloxacin (OFX) degradation rate by CuFeO2 {012} is four times faster than that of CuFeO2 {110} (0.0408 vs 0.0101 min–1). In CuFeO2 {012}-H2O2 system, OFX is completely removed at a pH range 3.2–10.1. The experimental results and theoretical simulations show that •OH is preferentially formed from the reduction of absorbed H2O2 by electron from CuFeO2 {012} due to suitable elongation of O–O (1.472 A) bond length in H2O2. By contrast, the O–O bond length is elongated from 1.468 to 3.290 A by CuFeO2 {110} facet, H2O2 tends to be d...

Surface Facet of CuFeO2 Nanocatalyst: A Key Parameter for H2O2 Activation in Fenton-Like Reaction and Organic Pollutant Degradation

Abstract The corrosion behavior of model Zr-based alloys at 500 °C is assessed by long term (up to 400 days) corrosion testing in an effort to evaluate their potential for use in the supercritical water reactor and to assess the influence of alloying elements on corrosion behavior. The corrosion weight gains from such systematic testing are seen to be a factor of five higher than those measured at 360 °C but the protectiveness ranking of the alloys is similar. Detailed characterization of the oxide layers to rationalize the differences in corrosion behavior was performed using synchrotron radiation and systematic differences are observed in protective and non-protective oxides, especially near the oxide–metal interface. The overall corrosion rate of the best Zr-based alloys compared favorably with those of other alloys being considered for use in the supercritical water reactor.

Zirconium alloys for supercritical water reactor applications : Challenges and possibilities

Rapid and sensitive detection of influenza virus is of soaring importance to prevent further spread of infections and adequate clinical treatment. Herein, an ultrasensitive colorimetric assay called magnetic nano(e)zyme-linked immunosorbent assay (MagLISA) is suggested, in which silica-shelled magnetic nanobeads (MagNBs) and gold nanoparticles are combined to monitor influenza A virus up to femtogram per milliliter concentration. Two essential strategies for ultrasensitive sensing are designed, i.e., facile target separation by MagNBs and signal amplification by the enzymelike activity of gold nanozymes (AuNZs). The enzymelike activity was experimentally and computationally evaluated, where the catalyticity of AuNZ was tremendously stronger than that of normal biological enzymes. In the spiked test, a straightforward linearity was presented in the range of 5.0 × 10–15–5.0 × 10–6g·mL–1 in detecting the influenza virus A (New Caledonia/20/1999) (H1N1). The detection limit is up to 5.0 × 10–12 g·mL–1 only by...

Magnetic Nanozyme-Linked Immunosorbent Assay for Ultrasensitive Influenza A Virus Detection.

We have investigated the reactions of H2O2 with Fe2O3, CuO, HfO2, CeO2 and Gd 2O3 in aqueous solution. The reactions rate constants at room temperature were determined. From the temperature depende ...

Catalytic decomposition of hydrogen peroxide on transition metal and lanthanide oxides

One of the main challenges for the nuclear power industry today is the disposal of spent nuclear fuel. One of the most developed methods for its long term storage is the Swedish KBS-3 concept where the spent fuel is sealed inside copper canisters and placed 500 meters down in the bedrock. Gamma radiation will penetrate the canisters and be absorbed by groundwater thereby creating oxidative radiolysis products such as hydrogen peroxide (H2O2) and hydroxyl radicals (HO˙). Both H2O2 and HO˙ are able to initiate corrosion of the copper canisters. In this work the kinetics and mechanism of reactions between the stable radiolysis product, H2O2, and copper and copper oxides were studied. Also the dissolution of copper into solution after reaction with H2O2 was monitored by ICP-OES. The experiments show that both H2O2 and HO˙ are present in the systems with copper and copper oxides. Nevertheless, these species do not appear to influence the dissolution of copper to the same extent as observed in recent studies in irradiated systems. This strongly suggests that aqueous radiolysis can only account for a very minor part of the observed radiation induced corrosion of copper.

Kinetics and mechanisms of reactions between H2O2 and copper and copper oxides.

Interfacial reactions between H2O2 and metal oxides are important in several fields but are yet not fully understood. Recently, tris(hydroxymethyl)aminomethane (Tris) was used as a probe in detecti ...

Evaluation of the O-2 and pH Effects on Probes for Surface Bound Hydroxyl Radicals

In this work, the reaction between H2O2 and tungsten powder in the presence of Tris(hydroxymethyl) aminomethane was studied experimentally. The production of hydroxyl radicals can be quantified indirectly by quantifying the scavenging product formaldehyde (CH2O). XRD, XPS, and SEM analysis shows that no significant structural or compositional changes occur after reaction. We compared H2O2 consumption and CH2O formation in both heterogeneous W(s)/H2O2/Tris system and homogeneous W(aq)/H2O2/Tris system. Increasing the amount of W powder leads to the increase in dissolution rate of W species, insignificant increase of H2O2 consumption rate and the decrease of final CH2O production. By contrast, the consumption rate of H2O2 increases as increasing the concentration of dissolved W species. Based on the experimental results, a mechanism of H2O2 reacting with W powder in the presence of Tris is proposed. The mechanism well explained the relationship between surface reactions and homogeneous Haber–Weiss peroxide ...

Kinetics and Mechanism of the Reaction between H2O2 and Tungsten Powder in Water

In this work, the surface reactivity of hydroxyl radicals formed upon catalytic decomposition of H2O2 on ZrO2 in the presence of Tris(hydroxymethyl) aminomethane was studied experimentally. Two sets of competition experiments were performed: the competition between H2O2 and Tris for the surface bound hydroxyl radical (HO ) and between O2 and H2O2 for the hydroxymethyl radical ( CH2OH) (precursor for formaldehyde). A 5-fold increase in initial concentration of Tris or H2O2 does not lead to a 5-fold increase in CH2O formation (only by a factor of 2–3 in the studied concentration range). The O2-dependent enhancement of the final production of CH2O becomes weaker upon increasing the initial concentration of H2O2 from 0.5 mM to 5 mM. The final production of CH2O becomes independent of the concentration of Tris when [Tris]0 is above 100 mM, i.e., the surface is saturated with Tris at this concentration. Based on the experimental results, a site-specific mechanism of H2O2 decomposition on the surface of ZrO2 was proposed. This model was used for numerical simulations of the dynamics of the reaction system. The kinetics was simulated using the kinetic simulation software Gepasi 3.0 and the results are in good agreement with the experimental observations.

Miao Yang

Papers

Catalytic decomposition of hydrogen peroxide on transition metal and lanthanide oxides

Kinetics and mechanisms of reactions between H2O2 and copper and copper oxides.

Evaluation of the O-2 and pH Effects on Probes for Surface Bound Hydroxyl Radicals

Kinetics and Mechanism of the Reaction between H2O2 and Tungsten Powder in Water

Surface reactivity of hydroxyl radicals formed upon catalytic decomposition of H2O2 on ZrO2