GIS-based identification and assessment of suitable meeting point locations for ride-sharing

Ride-Sharing or carpooling is a common means to utilize available but so far unused vehicle seat capacity. To establish a shared ride, it is necessary that the driver and the passengers agree on a meeting point. In most existing applications, the pickup location of a passenger is assumed to be on his or her doorstep. However, many people are willing to walk a certain distance to meet at a place where a safe and convenient boarding can be established, while at the same time the necessary detour of the driver can be kept acceptable. In this contribution we introduce an assessment scheme for meeting point locations based on results of an online survey retrieving the stated acceptance of meeting point locations and the relevance of the available facilities like parking places, seating, shelter and light. To this end, the infrastructure of a medium-sized European city is assumed to show exemplary how the amount and the distribution of suitable meeting point locations affects the performance and convenience of ride-sharing.DFG/GRK/193

Phase- and Surface Composition-Dependent Electrochemical Stability of Ir-Ru Nanoparticles during Oxygen Evolution Reaction

The increasing scarcity of iridium (Ir) and its rutile-type oxide (IrO$_{2}$), the current state-of-the-art oxygen evolution reaction (OER) catalysts, is driving the transition toward the use of mixed Ir oxides with a highly active yet inexpensive metal (Ir$_{x}$M$_{1-x}$O$_{2}$). Ruthenium (Ru) has been commonly employed due to its high OER activity although its electrochemical stability in Ir-Ru mixed oxide nanoparticles (Ir$_{x}$Ru$_{1-x}$O$_{2}$ NPs), especially at high relative contents, is rarely evaluated for long-term application as water electrolyzers. In this work, we bridge the knowledge gap by performing a thorough study on the composition- and phase-dependent stability of well-defined Ir$_{x}$Ru$_{1-x}$O$_{2}$ NPs prepared by flame spray pyrolysis under dynamic operating conditions. As-prepared NPs (Ir$_{x}$Ru$_{1-x}$O$_{y}$) present an amorphous coral-like structure with a hydrous Ir-Ru oxide phase, which upon post-synthetic thermal treatment fully converts to a rutile-type structure followed by a selective Ir enrichment at the NP topmost surface. It was demonstrated that Ir incorporation into a RuO$_{2}$ matrix drastically reduced Ru dissolution by ca. 10-fold at the expense of worsening Ir inherent stability, regardless of the oxide phase present. Hydrous Ir$_{x}$Ru$_{1-x}$O$_{y}$ NPs, however, were shown to be 1000-fold less stable than rutile-type Ir$_{x}$Ru$_{1-x}$O$_{2}$, where the severe Ru leaching yielded a fast convergence toward the activity of monometallic hydrous IrO$_{y}$. For rutile-type Ir$_{x}$Ru$_{1-x}$O$_{2}$, the sequential start-up/shut-down OER protocol employed revealed a steady-state dissolution for both Ir and Ru, as well as the key role of surface Ru species in OER activity: minimal Ru surface losses (<1 at. %) yielded OER activities for tested Ir$_{0.2}$Ru$_{0.8}$O2 equivalent to those of untested Ir$_{0.8}$Ru$_{0.2}$O2. Ir enrichment at the NP topmost surface, which mitigates selective subsurface Ru dissolution, is identified as the origin of the NP stabilization. These results suggest Ru-rich Ir$_{x}$Ru$_{1-x}$O$_{2}$ NPs to be viable electrocatalysts for long-term water electrolysis, with significant repercussions in cost reduction

Microkinetic Analysis of the Oxygen Evolution Performance at Different Stages of Iridium Oxide Degradation

The microkinetics of the electrocatalytic oxygen evolution reaction substantially determines the performance in proton-exchange membrane water electrolysis. State-of-the-art nanoparticulated rutile IrO$_{2}$ electrocatalysts present an excellent trade-off between activity and stability due to the efficient formation of intermediate surface species. To reveal and analyze the interaction of individual surface processes, a detailed dynamic microkinetic model approach is established and validated using cyclic voltammetry. We show that the interaction of three different processes, which are the adsorption of water, one potential-driven deprotonation step, and the detachment of oxygen, limits the overall reaction turnover. During the reaction, the active IrO$_{2}$ surface is covered mainly by *O, *OOH, and *OO adsorbed species with a share dependent on the applied potential and of 44, 28, and 20% at an overpotential of 350 mV, respectively. In contrast to state-of-the-art calculations of ideal catalyst surfaces, this novel model-based methodology allows for experimental identification of the microkinetics as well as thermodynamic energy values of real pristine and degraded nanoparticles. We show that the loss in electrocatalytic activity during degradation is correlated to an increase in the activation energy of deprotonation processes, whereas reaction energies were marginally affected. As the effect of electrolyte-related parameters does not cause such a decrease, the model-based analysis demonstrates that material changes trigger the performance loss. These insights into the degradation of IrO$_{2}$ and its effect on the surface processes provide the basis for a deeper understanding of degrading active sites for the optimization of the oxygen evolution performance

Increased Ir–Ir Interaction in Iridium Oxide during the Oxygen Evolution Reaction at High Potentials Probed by Operando Spectroscopy

The structure of IrO$_{2}$ during the oxygen evolution reaction (OER) was studied by operando X-ray absorption spectroscopy (XAS) at the Ir L$_{3}$-edge to gain insight into the processes that occur during the electrocatalytic reaction at the anode during water electrolysis. For this purpose, calcined and uncalcined IrO$_{2}$ nanoparticles were tested in an operando spectroelectrochemical cell. In situ XAS under different applied potentials uncovered strong structural changes when changing the potential. Modulation excitation spectroscopy combined with XAS enhanced the information on the dynamic changes significantly. Principal component analysis (PCA) of the resulting spectra as well as FEFF9 calculations uncovered that both the Ir L$_{3}$-edge energy and the white line intensity changed due to the formation of oxygen vacancies and lower oxidation state of iridium at higher potentials, respectively. The deconvoluted spectra and their components lead to two different OER modes. It was observed that at higher OER potentials, the well-known OER mechanisms need to be modified, which is also associated with the stabilization of the catalyst, as confirmed by in situ inductively coupled plasma mass spectrometry (ICP-MS). At these elevated OER potentials above 1.5 V, stronger Ir–Ir interactions were observed. They were more dominant in the calcined IrO$_{2}$ samples than in the uncalcined ones. The stronger Ir–Ir interaction upon vacancy formation is also supported by theoretical studies. We propose that this may be a crucial factor in the increased dissolution stability of the IrO$_{2}$ catalyst after calcination. The results presented here provide additional insights into the OER in acid media and demonstrate a powerful technique for quantifying the differences in mechanisms on different OER electrocatalysts. Furthermore, insights into the OER at a fundamental level are provided, which will contribute to further understanding of the reaction mechanisms in water electrolysis

Hierarchically Structured CuCo₂S₄ Nanowire Arrays as Efficient Bifunctional Electrocatalyst for Overall Water Splitting

Hydrogen produced from water splitting offers a green alternative to conventional energy such as fossil fuels. Herein, CuCo₂S₄ nanowire arrays were synthesized on a nickel foam substrate by a two-step hydrothermal approach and utilized as highly efficient bifunctional electrocatalyst for overall water splitting. The CuCo₂S₄ nanowire arrays were identified as an exceptionally active catalyst for the hydrogen evolution reaction (HER) in a basic solution with an extremely low overpotential of 65 mV to reach a current density of 10 mA/cm². The hierarchically structured CuCo₂S₄ electrode was also highly active toward the oxygen evolution reaction (OER), achieving a high current density of 100 mA/cm² at an overpotential of only 310 mV. Consequently, an alkaline electrolyzer constructed using CuCo₂S₄ nanowire arrays as both anode and cathode can realize overall water splitting with a current density of 100 mA/cm² at a cell voltage of 1.65 V, suggesting a promising bifunctional electrocatalyst for efficient overall water splitting

Hierarchically Structured Cu-Based Electrocatalysts with Nanowires Array for Water Splitting

We report here the fabrication of CuO nanowires and their use as efficient electrocatalyst for the oxygen evolution reaction (OER) or as precursor for preparation of Cu₃P nanowires for the hydrogen evolution reaction (HER). The surface-bound Cu­(OH)₂ nanowires are <i>in situ</i> grown on a three-dimensional copper foam (CF) by anodic treatment, which are then converted to CuO nanowires by calcination in air. The direct growth of nanowires from the underlying conductive substrate can eliminate the use of any conductive agents and binders, which ensures good electrical contact between the electrocatalyst and the conductive substrate. The hierarchically nanostructured Cu-based electrode exhibits excellent catalytic performance toward OER in 1 M KOH solution. Phosphorization of the CuO/CF electrode generates the Cu₃P/CF electrode, which can act as an excellent electrocatalyst for HER in 1 M KOH. An alkaline electrolyzer is constructed using CuO and Cu₃P nanowires coated copper foams as anode and cathode, which can realize overall water splitting with a current density of 102 mA/cm² at an applied cell voltage of 2.2 V

Highly Dispersed Mo₂C Nanoparticles Embedded in Ordered Mesoporous Carbon for Efficient Hydrogen Evolution

The development of non-noble metal-based electrocatalysts for the hydrogen evolution reaction (HER) has attracted increasing attention over recent years. As a promising HER catalyst candidate, the preparation of molybdenum carbide requires high temperature for carbothermal reduction, which often causes nanoparticles sintering, leading to low exposed active sites. In this work, highly dispersed β-Mo₂C nanoparticles of approximately 5 nm embedded in ordered mesoporous carbon (Mo₂C@OMC) have been synergistically synthesized. During the synthesis process, the resol precursor for OMC template could serve as carbon source for the formation of Mo₂C and mitigate the sintering of Mo₂C nanoparticles. The resultant well-defined Mo₂C possesses highly exposed active sites of approximately 26.5% and exhibits an excellent performance for the HER in both acidic and alkaline solutions. The synthetic procedure developed in this study may be extended to fabricate other metal carbide@OMC nanocomposites for the HER and other electrocatalytic applications