Dynamic electro-chemo-mechanical analysis at the metal-electrolyte interface

Im Rahmen dieser Arbeit wird der Zusammenhang zwischen der mechanischen Verformung und den elektrochemischen Vorgängen auf der Oberfläche von metallischen Elektroden experimentell untersucht. Zunächst wird die dynamische elektrochemisch-mechanische Analyse (DECMA) als eine präzise experimentelle Strategie entworfen und validiert, um während der zyklischen Voltammetrie die Modulation von Potential und Strom als Antwort auf die zyklisch variable elastische Dehnung zu untersuchen. Anschließend wird durch die Beobachtung der Modulation des Reaktions-Stroms während der Dehnungszyklen der Elektrode auch die mechanisch modulierte Katalyse experimentell untersucht. Die Studien konzentrieren sich auf einen Modell-Prozess: Die Evolution der Reaktion mit Wasserstoff (engl.: HER) an 111-texturierten, polykrstallinen Goldund Platin-Dünnfilmelektroden. Aus den Messungen ergeben sich sowohl die Dehnungs-Abhängigkeit der Wasserstoff-Adsorptionsenthalpie als auch der Aktivierungsenthalpie der Reaktion bei HER. Als wesentliche Schlussfolgerung ergibt sich, dass die Reaktionsrate der heterogenen Katalyse deutlich variiert, wenn die Oberfläche elastisch in der Tangentialebene gedehnt wird. Dies eröffnet neue Perspektiven für die gezielte Abstimmung der elastischen Verformung von Katalysatoren – in anderen Worten, der Gitter-Parameter der Oberflächen-Atome – mit der Folge der Verstärkung ihrer Reaktivität. Diese Vorgehensweise der Beobachtung von mechanisch modulierten Reaktionsraten bei der Elektrokatalyse kann auch auf elektrokatalytische Reaktionen von Interesse angewendet werden. Es ist beabsichtigt, dies als ein Werkzeug für die Untersuchung der dehnungsabhängigen Katalyse und des Reaktionsmechanismus einzuführen.The link between the mechanical deformation and the electrochemical processes on the surfaces of metal electrodes is experimentally studied. Firstly, Dynamic Electro-Chemo-Mechanical Analysis (DECMA) is designed and validated as a precise experimental strategy to investigate the potential- and current- modulation in response to the cyclic elastic strain during the cyclic voltammetry. Secondly, the mechanically modulated catalysis is investigated experimentally by monitoring the reaction current modulation during the strain cycles on the electrode. As a model process in study, the hydrogen evolution reaction (HER) is focused in experiments on 111-textured, polycrystalline gold and platinum thin film electrodes. The results show the strain-dependence of the hydrogen adsorption enthalpy as well as the reaction activation enthalpy in HER. The main conclusion is that the reaction rate of heterogeneous catalysis varies considerably when the surface is elastically strained in the tangent plane. This opens a new perspective on tuning the elastic deformation - in other words, tuning the lattice parameter of surface atoms - of catalysts, so as to enhance their reactivity. The approach of monitoring mechanically modulated reaction rates in electrocatalysis can be also applied to the electrocatalytic reactions of interest. It is prospected as a tool for studying strain-dependent catalysis and for investigating reaction mechanism

Improvement of Hydrogen Desorption Characteristics of MgH₂ With Core-shell Ni@C Composites

Magnesium hydride (MgH2) has become popular to study in hydrogen storage materials research due to its high theoretical capacity and low cost. However, the high hydrogen desorption temperature and enthalpy as well as the depressed kinetics, have severely blocked its actual utilizations. Hence, our work introduced Ni@C materials with a core-shell structure to synthesize MgH2-x wt.% Ni@C composites for improving the hydrogen desorption characteristics. The influences of the Ni@C addition on the hydrogen desorption performances and micro-structure of MgH2 have been well investigated. The addition of Ni@C can effectively improve the dehydrogenation kinetics. It is interesting found that: i) the hydrogen desorption kinetics of MgH2 were enhanced with the increased Ni@C additive amount; and ii) the dehydrogenation amount decreased with a rather larger Ni@C additive amount. The additive amount of 4 wt.% Ni@C has been chosen in this study for a balance of kinetics and amount. The MgH2-4 wt.% Ni@C composites release 5.9 wt.% of hydrogen in 5 min and 6.6 wt.% of hydrogen in 20 min. It reflects that the enhanced hydrogen desorption is much faster than the pure MgH2 materials (0.3 wt.% hydrogen in 20 min). More significantly, the activation energy (EA) of the MgH2-4 wt.% Ni@C composites is 112 kJ mol−1, implying excellent dehydrogenation kinetics

Electrochemical Performance of Iron Oxide Nanoflakes on Carbon Cloth under an External Magnetic Field

In this work, the iron oxide (Fe2O3) nanoflakes on carbon cloth (Fe2O3@CC) were triumphantly prepared and served as the electrode of supercapacitors. By applying an external magnetic field, we first find that the magnetic field could suppress the polarization phenomenon of electrochemical performance. Then, the influences of the mono-/bi-valent cations on the electrochemical properties of the Fe2O3@CC were investigated under a large external magnetic field (1 T) in this work. The chemical valences of the cations in the aqueous electrolytes (LiNO3 and Ca(NO3)2) have almost no influences on the specific capacitance at different scan rates. As one of important parameters to describe the electrochemical properties, the working potential window of the Fe2O3@CC electrode was also investigated in this work. The broad potential window in room-temperature molten salt (LiTFSI + LiBETI (LiN(SO2CF3)2 + LiN(SO2C2F5)2)) has been obtained and reached 1.2 V, which is higher than that of the traditional aqueous electrolyte (~0.9 V)

The Effect of an External Magnetic Field on the Electrochemical Capacitance of Nanoporous Nickel for Energy Storage

This work investigates the effect of a magnetic field on the electrochemical performance of nanoporous nickel (np-Ni). We first compare the electrochemical capacitance of np-Ni electrodes, which were prepared using the chemical dealloying strategy under different magnetic flux densities (B = 0, 500 mT). Our experimental data show that np-Ni500 prepared under an external magnetic field of 500 mT exhibits a much better electrochemical performance, in comparison with that (np-Ni0) prepared without applying a magnetic field. Furthermore, the specific capacitance of the np-Ni0 electrode could be further enhanced when we increase the magnetic flux densities from 0 T to 500 mT, whereas the np-Ni500 electrode exhibits a stable electrochemical performance under different magnetic flux densities (B = 0 mT, 300 mT, 500 mT). This could be attributed to the change in the electrochemical impedance of the np-Ni0 electrode induced by an external magnetic field. Our work thus offers an alternative method to enhance the electrochemical energy storage of materials