Gas diffusion electrodes are essential components of common fuel and electrolysis cells but are typically made from graphitic carbon or metallic materials, which do not allow light transmittance and thus limit the development of gas‐phase based photoelectrochemical devices. Herein, the simple and scalable preparation of F‐doped SnO2 (FTO) coated SiO2 interconnected fiber felt substrates is reported. Using 2–5 µm diameter fibers at a loading of 4 mg cm−2, the resulting substrates have porosity of 90%, roughness factor of 15.8, and Young's Modulus of 0.2 GPa. A 100 nm conformal coating of FTO via atmospheric chemical vapor deposition gives sheet resistivity of 20 ± 3 Ω sq−1 and loss of incident light of 41% at illumination wavelength of 550 nm. The coating of various semiconductors on the substrates is established including Fe2O3 (chemical bath deposition), CuSCN and Cu2O (electrodeposition), and conjugated polymers (dip coating), and liquid‐phase photoelectrochemical performance commensurate with flat FTO substrates is confirmed. Finally, gas phase H2 production is demonstrated with a polymer semiconductor photocathode membrane assembly at 1‐Sun photocurrent density on the order of 1 mA cm−2 and Faradaic efficiency of 40%.

Metallic electrodes based on iron, nickel, and/or cobalt have re-emerged as promising cost-effective anodes for the alkaline oxygen evolution reaction (OER) due to their simplicity and their in situ formation of a highly active oxy-hydroxide surface catalyst layer, which exhibits state-of-the-art overpotentials for the OER. However, the effect of alloy composition has not been systematically studied. Herein, using metallic anodes with defined Fe–Ni–Co atomic ratios prepared via arc melting, we report the relationship between the initial alloy composition, the OER performance, and the emergent active catalyst composition. After 50 h operation at 0.5 A cm–2 the most active initial alloys (having a moderate amount of cobalt <40 at. %, an iron proportion between 30 and 80 at. % and a nickel ratio below 60 at. %) gave average overpotentials for 10 mA cm–2 ca. 300–320 mV and Tafel slopes of 35–50 mV dec–1. Iron and nickel-rich alloys performed poorer. The oxyhydroxide OER catalyst formed on the anode surface generally showed an increased concentration of Co and Ni and a depletion of Fe compared to the initial metal composition, giving the most active OER catalyst at a composition of Ni and Co of ca. 40 at. % with Fe at ca. 20 at. %. However, the initial alloy composition of Fe12.5Co12.5Ni75, showed a nearly invariant surface metal composition, indicating this as the most stable composition. Further analysis of the surface identified no correlation of the mass of metals leached from the anode surface, the electrochemically active surface area, or the presence of active Ni2+/3+ redox surface sites to the OER performance suggesting these factors do not influence the results.

Dispersion and aggregation of nanomagnetite (Fe3O4) and silica (SiO2) particles are of high importance in various applications, such as biomedicine, nanoelectronics, drug delivery, flotation, and pelletization of iron ore. In directly probing nanomagnetite–silica interaction, atomic force microscopy (AFM) using the colloidal probe technique has proven to be a suitable tool. In this work, the interaction between nanomagnetite and silica particles was measured with AFM in aqueous Ca2+ solution at different pH levels. This study showed that the qualitative changes of the interaction forces with pH and Ca2+ concentrations were consistent with the results from zeta-potential measurements. The repulsion between nanomagnetite and silica was observed at alkaline pH and 1 mM Ca2+ concentration, but no repulsive forces were observed at 3 mM Ca2+ concentration. The interaction forces on approach were due to van der Waals and electrical double-layer forces. The good fitting of experimental data to the DLVO model and simulations supported this conclusion. However, contributions from non-DLVO forces should also be considered. It was shown that an increase of Ca2+ concentration from 1 to 3.3 mM led to a less pronounced decrease of adhesion force with increasing pH. A comparison of measured and calculated adhesion forces with a few contact mechanics models demonstrated an important impact of nanomagnetite layer nanoroughness.