Bismuth vanadate (BVO) is a promising metal oxide semiconductor for photoelectrochemical water oxidation. In this study, BVO was deposited using atomic layer deposition (ALD) of alternating films of bismuth and vanadium oxides. A novel Bi-alkoxide precursor was used to enable precise control of stoichiometry along the spectrum of Bi-rich to V-rich compositions, and phase-pure monoclinic BVO films were obtained after postannealing. A planar photoanode composed of an undoped 41.8 nm BVO thin-film electrode with an ALD SnO2 buffer layer produced a photocurrent density of 2.24 mA/cm2 at 1.23 V vs RHE. ALD was used to conformally coat BVO and SnO2 on a ZnO nanowire template to produce core–shell photoanodes exhibiting a 30% increase in photocurrent density (2.9 mA/cm2 at 1.23 V) relative to planar control electrodes. This is the highest photocurrent reported to date for an ALD-deposited photoanode, and provides a pathway toward rational design of 3-D nanostructured photoelectrode architectures.

Polyurethane potting compounds and sealants, widely used as encapsulating and protective barriers, are usually applied to substrates after precoating substrate surfaces with primers. While the use of primers is known to improve adhesion properties of polyurethanes, fundamental mechanisms of adhesion enhancement are not fully understood due to the difficulties of direct observations at buried interfaces. Interfacial properties like adhesion are determined by interfacial molecular structures. In this study, sum frequency generation (SFG) vibrational spectroscopy was applied to investigate interfacial molecular structures in situ between a polyurethane potting compound and an isocyanate-based primer. The SFG signals of isocyanate groups from the primer initially were observed at the interface but disappeared after 16 h of polyurethane cure time. The following SFG experiments confirmed that interfacial reaction occurred at the interface between the polyurethane potting compound and the primer. Attenuated total reflectance (ATR)-FTIR spectroscopy and 180° peel tests were utilized as complementary techniques to support the SFG analyses. The results indicate that the formation of chemical bonds at the interface were responsible for the enhancement of adhesion. This study aims to help build on fundamental design principles toward the development of polymer materials with improved mechanical performance and other macroscopic interfacial properties.

The binding constants and rate constants for desorption of the modified molecular dye [Ru(bpy)] anchored by either phosphonate or hydroxamate on the bipyridine ligand to anatase TiO and WO have been measured. In aqueous media at pH 1-10, repulsive electrostatic interactions between the negatively charged anchor and the negatively charged surface govern phosphonate desorption under neutral and basic conditions for TiO anatase due to the high acidity of phosphonic acid (p K = 5.1). In contrast, the lower acidity of hydroxamate (p K = 6.5, p K = 9.1) leads to little change in adsorption/desorption properties as a function of pH from 1 to 7. The binding constant for hydroxamate is 10 in water, independent of pH in this range. These results are true for WO as well, but are not reported at pH > 4 due to its Arrhenius acidity. Kinetics for desorption as a function of pH are reported, with a proposed mechanism for phosphonate desorption at high pH being the electrostatic repulsion of negative charges between the surface and the anionic anchor. Further, the hydroxamic acid anchor itself is likely the site of quasi-reversible redox activity in [Ru(bpy)(2,2'-bpy-4,4'-(C(O)N(OH)))], which does not lead to any measurable deterioration of the complex within 2 h of dark cyclic voltammogram scans in aqueous media. These results posit phosphonate as the preferred anchoring group under acidic conditions and hydroxamate for neutral/basic conditions.

We analyze the stability of the non-heme water oxidation catalyst (WOC), Fe(bpmcn)Cl toward oxygen and illumination under nonaqueous and acidic conditions. Fe(bpmcn)Cl has been previously used as a C-H activation catalyst, a homogeneous WOC, and as a cocatalyst anchored to WO for photoelectrochemical water oxidation. This paper reports that the ligand dissociates at pH 1 with a rate constant k = 19.8(2) × 10 min, resulting in loss of catalytic activity. The combination of UV-vis experiments, H NMR spectroscopy, and cyclic voltammetry confirm free bpmcn and Fe present in solution under acidic conditions. Even under nonaqueous conditions, both oxygen and illumination together show slow oxidation of iron over the course of a few hours, consistent with forming an Fe-O intermediate as corroborated by resonance-enhanced Raman spectroscopy, with a rate constant of k = 3.03(8) × 10 min. This finding has implications in both the merits of non-heme iron complexes as WOCs as well as cocatalysts in photoelectrochemical schemes: the decomposition mechanisms may include both anchoring group hydrolysis and instability under illumination.