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This approach suggests a hybrid bimetallic organic frameworks (H-biMOF) as electrocatalyst for the oxygen evolution reaction (OER) under alkaline conditions. A H-biMOF including cobalt (II) and nickel (II) was synthesized with terephthalic acid (Tp) as a linker using one-pot solvothermal method. The morphological study with microscopy techniques shows hexagonal rod-like structures for pure cobalt MOF, wood-shaving-like structures for pure nickel MOF and hexagonal nanosheets coated by wood-shaving-like structures with for H-biMOF. The structure of H-biMOF was confirmed by XRD showing both pure Co and Ni MOFs in the pattern. The catalytic OER ability of all samples was evaluated using electrochemical methods. The best performance was achieved for a H-biMOF made from a 3:1 starting salt ratio of cobalt and nickel (CoTp 3:1(Ni)). The OER catalytic activity of CoTp 3:1(Ni) demonstrates a low overpotential of 371 mV and a Tafel slope of 53.6 mV dec−1 (at a current density of 10 mA cm−2). The high catalytic activity of the biMOF through OER is related to the high number of active sites and suitable mass transport properties providing reactatnts to increase the current density at a given potential.

The physical swelling of uncharged graphite composite electrodes due to electrolyte-binder interactions is investigated by scanning electrochemical microscopy (SECM) using 2,5-di-tert-butyl-1,4,-dimethoxybenzene as a redox mediator. A series of approach curves at the same location is conducted in order to quantify in situ and locally the physical swelling. The film thickness change dfilm amounted to 9.1 mm on average for a 80 mm thick uncharged graphite composite electrode in LP40 electrolyte between 1.1 and 5.9 h. Curves of dfilm vs. t usually reach a saturation within 12 h. The swelling ratio CH varies from 0.3% to 17.6% for uncharged graphite composite electrodes from the same batch in the same electrolyte. In contrast, the 8 mm thick polyvinylidene fluoride (PVDF) model sample swelled by CH = 99%. Approach curves demonstrate that swelling of the PVDF is the main cause for the physical swelling of uncharged graphite composite electrodes. Both PVDF model sample and uncharged graphite composite electrodes show locally different swelling ratios by SECM imaging. Based on these results a swelling model is proposed, where the uncharged graphite composite electrode swells physically on average by at least CH = 11% and the local topography is changing during swelling.

The passivating properties of solid electrolyte interphases (SEI) at metallic lithium were characterized using the feedback mode of scanning electrochemical microscopy (SECM) and 2,5-di-tert-butyl-1,4-dimethoxybenzene (DBDMB) as redox mediator at OCP. The SEI at Li allows electron transfer toward DBDMB with finite rate. In comparison to charged graphite composite electrodes, the electron transfer rate tends to be smaller at Li. Both, graphite composite and Li electrodes, show a local variation of electron transfer rates and temporal changes within a time span of hours. The long-term changes of SEI passivity at metallic Li are dependent on the solvents in the liquid electrolyte. In addition, significant short-term changes of SEI passivity occur at both electrodes. However, the frequency of such events is smaller for metallic Li compared to graphite. A strong decrease of SEI passivity and a strong increase of fluctuations in the passivating properties are observed when the microelectrode mechanically touches the metallic Li and damages the SEI. The changes of SEI passivity by a mechanical touch are orders of magnitude larger compared to spontaneous changes. A local SEI damage by the microelectrode decreases not only the SEI passivity locally, but also a few hundreds of mm apart.

A native oxide film on the biphasic alloy Ti6A14V was studied with scanning electrochemical microscopy (SECM). This alloy is commonly used for biomedical applications due to its biocompatibility and mechanical properties. The heterogeneously composed, n-semiconducting oxide film is of particular interest as biological systems are in contact only with these oxides and immunological rejection mechanisms may be connected to their electrochemical properties. Auger electron spectroscopy showed that the elemental composition of the oxide films on the a and β phase differ from each other. Approach curves were recorded above individual grains of the a phase in the feedback mode with several redox mediators. They were selected to cover a wide range of redox potentials for a better understanding of the surface kinetics of the oxide layer. The electron-transfer kinetics changed strongly depending on the redox potential of the mediator with respect to the energetic position of the bandgap of the oxide film. Predictions about the value of the flatband potential on an individual phase were derived from these experiments. Furthermore, SECM images were recorded to laterally resolve different electrochemical properties of the oxide film originating from the heterogeneous composition of the oxide on both phases.