A multifunctional electrocatalytic composite was synthesized for use as a generic catalytic material in the polymer electrolyte membrane (PEM) type reactors, working in either fuel cell, direct methanol fuel cell, or electrolyzer mode. It is constructed from graphene sheets evenly covered with TiONx on which PtCu, Ir, and Ru nanoparticles are immobilized. It enables high performances for oxygen reduction, hydrogen and methanol oxidation, and also hydrogen and oxygen evolution. Its activity is either higher or comparable to the monofunctional benchmark catalysts, namely, Pt, PtRu, and Ir nanoparticles. An important part of this study is the advanced electrochemical degradation investigation. With the use of an electrochemical flow cell coupled to ICP-MS and combining these results with identical location electron microscopy, we reveal not only potential shortcomings but also opportunities for our material. As a result, we also put forward general guidelines for the appropriate use of multifunctional electrocatalysts.
COBISS.SI-ID: 40295429
With Liquid-Cell Transmission Electron Microscopy (LCTEM) we can observe the kinetic processes taking place in nanoscale materials that are in a solvated environment. However, the beam-driven solvent radiolysis, which results from the microscope's high-energy electron beam, can dramatically influence the dynamics of the system. Recent research suggests that radical-induced redox chemistry can be used to investigate the various redox-driven dynamics for a wide range of functional nanomaterials. In view of this, the interplay between the formation of various highly reactive radiolysis species and the nanomaterials under investigation needs to be quantified in order to formulate new strategies for nanomaterials research. We have developed a comprehensive radiolysis model by using the electron-dose rate, the temperature of the solvent, the H2 and O2 gas saturation concentrations and the pH values as the key variables. These improved kinetic models make it possible to simulate the material's specific radical-induced redox reactions. As in the case of the Au model system, the kinetic models are presented using Temperature/Dose-rate Redox potential (TDR) diagrams, which indicate the equilibrium [Au0]/[Au+] concentration ratios that are directly related to the temperature-/dose-rate-dependent precipitation or dissolution regions of the Au nanoparticles. Our radiolysis and radical-induced redox models were successfully verified using previously reported data from low-dose experiments with ? radiation and experimentally via TDR-dependent LCTEM. The presented study represents a holistic approach to the radical-induced redox chemistry in LCTEM, including the complex kinetics of the radiolysis species and their influence on the redox chemistry of the materials under investigation, which are represented here by Au nanoparticles.
COBISS.SI-ID: 32582439
Catalytic properties of advanced functional materials are determined by their surface and near-surface atomic structure, composition, morphology, defects, compressive and tensile stresses, etc; also known as a structure–activity relationship. The catalysts structural properties are dynamically changing as they perform via complex phenomenon dependent on the reaction conditions. In turn, not just the structural features but even more importantly, catalytic characteristics of nanoparticles get altered. Definitive conclusions about these phenomena are not possible with imaging of random nanoparticles with unknown atomic structure history. Using a contemporary PtCu-alloy electrocatalyst as a model system, a unique approach allowing unprecedented insight into the morphological dynamics on the atomic-scale caused by the process of dealloying is presented. Observing the detailed structure and morphology of the same nanoparticle at different stages of electrochemical treatment reveals new insights into atomic-scale processes such as size, faceting, strain and porosity development. Furthermore, based on precise atomically resolved microscopy data, Kinetic Monte Carlo (KMC) simulations provide further feedback into the physical parameters governing electrochemically induced structural dynamics. This work introduces a unique approach toward observation and understanding of nanoparticles dynamic changes on the atomic level and paves the way for an understanding of the structure–stability relationship.
COBISS.SI-ID: 6623002
In the past decades, there has been an ongoing search for tailor-made active metal nanoparticles for the use as electrocatalysts. An upcoming versatile and green method for the synthesis of nanoparticles is electrodeposition. However, the state-of-the-art electrodeposited metal particle sizes are in the range of 50–200?nm. Production of high surface area metallic electrocatalysts with small particle sizes is a serious limitation of electrodeposition, i.e., the Gordian Knot. In this article, we present a novel and facile approach by combining electrodeposition with controlled cathodic corrosion to obtain tailor-made nanoparticles down to the single atom. Via controlled cathodic corrosion treatment, relatively big electrodeposited metal nanoparticles (Ag, Pt, Pd, Ni, etc.) are effectively broken down and evenly dispersed on the carbon electrode surface, without particle detachment. The same electrochemical phenomenon is also utilized for in-situ electrocatalysts reactivation, referred as redispersion, of the degraded electrocatalysts. The two new concepts open new possibilities and applications for the electrodeposition as a metal nanoparticles production method and in-situ regeneration solutions for electrochemical energy conversion reactors like fuel cells and electrolyzers; as the two pillars of a near-future transition to sustainable energy.
COBISS.SI-ID: 6306074
Iridium-based particles, regarded as the most promising proton exchange membrane electrolyzer electrocatalysts, were investigated by transmission electron microscopy and by coupling of an electrochemical flow cell (EFC) with online inductively coupled plasma mass spectrometry. Additionally, studies using a thin-film rotating disc electrode, identical location transmission and scanning electron microscopy, as well as X-ray absorption spectroscopy have been performed. Extremely sensitive online time-and potential-resolved electrochemical dissolution profiles revealed that Ir particles dissolve well below oxygen evolution reaction (OER) potentials, presumably induced by Ir surface oxidation and reduction processes, also referred to as transient dissolution. Overall, thermally prepared rutile-type IrO2 particles are substantially more stable and less active in comparison to as-prepared metallic and electrochemically pretreated (E-Ir) analogues. Interestingly, under OER-relevant conditions, E-Ir particles exhibit superior stability and activity owing to the altered corrosion mechanism, where the formation of unstable Ir()IV) species is hindered. Due to the enhanced and lasting OER performance, electrochemically pre-oxidized E-Ir particles may be considered as the electrocatalyst of choice for an improved low-temperature electrochemical hydrogen production device, namely a proton exchange membrane electrolyzer.
COBISS.SI-ID: 6203674