Efficient and stable immobilisation and wiring of bioelectrocatalysts on specific electrode surfaces for bioelectrocatalytic applications

Die vorliegende Arbeit beschreibt die vielfältigen Anwendungsmöglichkeiten von mit (Photo)Bioelektrokatalysatoren modifizierten Elektroden. Im ersten Teil der Arbeit wurden die Interaktionen von Redoxpolymer/Enzymfilmen mit verschiedenen Elektroden sowie deren Einfluss auf die Stabilität von amperometrischen Biosensoren untersucht und diese entsprechend optimiert. Dadurch konnte ein neuartiges Messkonzept für nahezu gleichgewichtsbasierte amperometrische Biosensoren entwickelt werden. Der zweite Teil der Arbeit schildert die Oberflächenstrukturierung von Elektroden und deren anschließende Modifikation mit (Photo)Bioelektrokatalysatoren. Die Verwendung eines stetig verbesserten Sprühbeschichtungssystem führte zur Entwicklung und Herstellung verschiedener transparenter hochleistungsfähiger (Photo)Bioelektroden. Diese eignen sich unter anderem für die Verwendung in neuartigen Geräten zur Gesundheitsüberwachung sowie als Biosuperkondensatoren für hybride Energieerzeugung und -speicherung

Tuning light‐driven water splitting efficiency of Mo‐doped BiVO_4\_4

We present airbrush spray‐coating as a reproducible method for the preparation of Mo‐doped BiVO$\_4$ (Mo : BiVO$\_4$) as photoabsorber with different layer thicknesses and Mo content. Optimisation of layer thickness is aiming on diminishing limitations by the electronic conductivity within the photoabsorber, thus increasing the incident photon to current efficiency (IPCE) of the samples. Furthermore, the Mo to V ratio leading to the highest photocurrent density was determined, and the optimised Mo : BiVO$\_4$ samples were decorated with a variety of oxygen evolution reaction (OER) electrocatalysts such as cobalt phosphate and layered double hydroxides. A mass loading gradient of Ni−Fe LDH was sprayed on top of the Mo : BiVO$\_4$ photoanode for optimisation of the OER catalyst loading. The photocurrent density was enhanced by up to 5.8 times at 0.8 V vs. RHE in comparison with the pristine Mo : BiVO$\_4$ sample in absence of any OER electrocatalyst

Scalable Fabrication of Biophotoelectrodes by Means of Automated Airbrush Spray-Coating

The fabrication and electrochemical evaluation of transparent photoelectrodes consisting of Photosystem I (PSI) or Photosystem II (PSII) is described, which are embedded and electrically wired by a redox polymer. The fabrication process is performed by an automated airbrush-type spray coating system, which ensures controlled and scalable electrode preparation. As proof of concept, electrodes with a surface area of up to 25 cm2 were prepared. The macro-porous structure of the indium tin oxide electrodes allows a high loading of the photoactive protein complexes leading to enhanced photocurrents, which are essential for potentially technologically relevant solar-powered devices. In addition, we show that unpurified crude PSII extracts, which can be provided in comparatively high yields for electrode modification, are suitable for photoelectrode fabrication with comparable photocurrent densities

Importance of catalyst–photoabsorber interface design configuration on the performance of Mo-doped BiVO4BiVO_{4} water splitting photoanodes

Photoelectrochemical water splitting is mostly impeded by the slow kinetics of the oxygen evolution reaction. The construction of photoanodes that appreciably enhance the efficiency of this process is of vital technological importance towards solar fuel synthesis. In this work, Mo-modified $BiVO_{4}$ (Mo:$BiVO_{4}$), a promising water splitting photoanode, was modified with various oxygen evolution catalysts in two distinct configurations, with the catalysts either deposited on the surface of Mo:$BiVO_{4}$ or embedded inside a Mo:$BiVO_{4}$ film. The investigated catalysts included monometallic, bimetallic, and trimetallic oxides with spinel and layered structures, and nickel boride ($Ni_{x}B$). In order to follow the influence of the incorporated catalysts and their respective properties, as well as the photoanode architecture on photoelectrochemical water oxidation, the fabricated photoanodes were characterised for their optical, morphological, and structural properties, photoelectrocatalytic activity with respect to evolved oxygen, and recombination rates of the photogenerated charge carriers. The architecture of the catalyst-modified Mo:$BiVO_{4}$ photoanode was found to play a more decisive role than the nature of the catalyst on the performance of the photoanode in photoelectrocatalytic water oxidation. Differences in the photoelectrocatalytic activity of the various catalyst-modified Mo:$BiVO_{4}$ photoanodes are attributed to the electronic structure of the materials revealed through differences in the Fermi energy levels. This work thus expands on the current knowledge towards the design of future practical photoanodes for photoelectrocatalytic water oxidation

Tuning light-driven water oxidation efficiency of molybdenum-doped BiVO4BiVO_{4} by means of multicomposite catalysts containing nickel, iron, and chromium oxides

Mo-doped $BiVO_{4}$ has emerged as a promising material for photoelectrodes for photoelectrochemical water splitting, however, still shows a limited efficiency for light-driven water oxidation. We present the influence of an oxygen-evolution catalyst composed of Ni, Fe, and Cr oxides on the activity of Mo:$BiVO_{4}$ photoanodes. The photoanodes are prepared by spray-coating, enabling compositional and thickness gradients of the incorporated catalyst. Two different configurations are evaluated, namely with the catalyst embedded into the Mo:$BiVO_{4}$ film or deposited on top of it. Both configurations provide a significantly different impact on the photoelectrocatalytic efficiency. Structural characterisation of the materials by means of SEM, TEM and XRD as well as the photoelectrocatalytic activity investigated by means of an optical scanning droplet cell and $\textit {in situ}$ detection of oxygen using scanning photoelectrochemical microscopy are presented

Aerosol‐based synthesis of multi‐metal electrocatalysts for oxygen evolution and glycerol oxidation

Discovery of new catalysts is crucial for future growth and development of environmentally friendly energy conversion processes e. g. the production of hydrogen by water electrolysis. We developed an aerosol-based synthesis technique as a comparatively fast and facile method to prepare multi-metal catalysts. 22 different quinary metal compositions were synthesized and investigated with respect to their activity for the oxygen evolution (OER) and the glycerol oxidation (GOR) reactions. The impact of the element composition and the homogeneous distribution of the elements in the particles on catalytic performance were evaluated. The highest activity for OER was found for $Co_{20}Cu_{20}Ni_{20}Fe_{20}Zn_{20}$. For GOR, Ag-containing catalysts were the most active, however, in most cases Ag was locally enriched and not homogeneously mixed with the other metals in the particles. Ag-based catalysts outperformed similar compositions containing one or more noble metals. The GOR selectivity of selected catalysts during long-term electrolysis was also investigated and it was shown that varying the catalyst composition via aerosol-based synthesis is a potential way to modulate the GOR selectivity