Molecular catalysts can promote ammonia oxidation, providing mechanistic insights into the electrochemical N₂ cycle for a carbon-free fuel economy. We report the ammonia oxidation activity of carbon anodes functionalized with the oligomer {[Ru^II(bda-κ-N ² O ²)(4,4'-bpy)]₁₀(4,4'-bpy)}, Rubda-10, where bda is [2,2'-bipyridine]-6,6'-dicarboxylate and 4,4'-bpy is 4,4'-bipyridine. Electrocatalytic studies in propylene carbonate demonstrate that the Ru-based hybrid anode used in a 3-electrode configuration transforms NH₃ to N₂ and H₂ in a 1:3 ratio with near-unity faradaic efficiency at an applied potential of 0.1 V vs Fc^+/0, reaching turnover numbers of 7500. X-ray absorption spectroscopic analysis after bulk electrolysis confirms the molecular integrity of the catalyst. Based on computational studies together with electrochemical evidence, ammonia nucleophilic attack is proposed as the primary pathway that leads to critical N-N bond formation.

Intensity-modulated photocurrent spectroscopy (IMPS) has been largely employed in semiconductor characterization for solar energy conversion devices to probe the operando behavior with widely available facilities. However, the implementation of IMPS data analysis to complex structures, whether based on the physical rate constant model (RCM) or the assumption-free distribution of relaxation times (DRT), is generally limited to a semi-quantitative description of the charge carrier kinetics of the system. In this study, a new algorithm for the analysis of IMPS data is developed, providing unprecedented time resolution to the investigation of μs to s charge carrier dynamics in semiconductor-based systems used in photoelectrochemistry and photovoltaics. The algorithm, based on the previously developed DRT analysis, is herein modified with a Lasso regression method and available to the reader free of charge. A validation of this new algorithm is performed on a α-Fe₂O₃ photoanode for photoelectrochemical water splitting, identified as a standard platform in the field, highlighting multiple potential-dependent charge transfer paths, otherwise hidden in the conventional IMPS data analysis.

WO₃/BiVO₄ films obtained by electrochemical deposition of BiVO₄ over mesoporous WO₃ were applied to the photoelectrochemical degradation of selected emerging contaminants (ketoprofen and levofloxacine) in aqueous solutions. The WO₃/BiVO₄ films in this work are characterized by a mesoporous morphology with a maximum photoconversion efficiency >40% extending beyond 500 nm in Na₂SO₄ electrolytes. Oxygen was found to be the dominant water oxidation product (ca. 90% faradaic yield) and no evidence for the photogeneration of OH radicals was obtained. Nevertheless, both 10 ppm levofloxacine and ketoprofen could be degraded at WO₃/BiVO₄ junctions upon a few hours of illumination under visible light. However, while levofloxacine degradation intermediates were progressively consumed by further oxidation at the WO₃/BiVO₄ interface, ketoprofen oxidation byproducts, being stable aromatic species, were found to be persistent in aqueous solution even after 15 hours of solar simulated illumination. This indicates that, due to the lower oxidizing power of photogenerated holes in BiVO₄ and a different water oxidation mechanism, the employment of WO₃/BiVO₄ in photoelectrochemical environmental remediation processes is much less universal than that possible with wider band gap semiconductors such as TiO₂ and WO₃.

The understanding of charge carrier dynamics in complex heterojunctions is of the utmost importance for the performance optimization of photoelectrochemical cells, especially in operando. Intensity‐modulated photocurrent spectroscopy (IMPS) is a powerful tool to this aim, but the information content provided by this technique can be further enhanced by selectively probing each layer of complex heterojunctions by means of multiple excitation sources. Herein, the charge carrier dynamics of a WO₃/BiVO₄/CoFe–PB heterojunction, used in a conventional three electrode cell for water splitting, is studied using wavelength‐dependent IMPS (WD‐IMPS). The proposed data analysis allows us to identify the occurrence of interface recombination processes affecting the semiconductor junction, as well as the positive contribution of the inorganic complex catalyst on the charge separation efficiency of the BiVO₄ layer. The deep understanding of the fate of charge carriers in the studied photoanode validates WD‐IMPS as a straightforward method to widen the understanding of such structures.

Metal halide perovskites (MHPs) are disruptive materials for a vast class of optoelectronic devices. The presence of electronic trap states has been a tough challenge in terms of characterization and thus mitigation. Many attempts based on electronic spectroscopies have been tested, but due to the mixed electronic-ionic nature of MHP conductivity, many experimental results retain a large ambiguity in resolving electronic and ionic charge contributions. Here we adapt a method, previously used in highly resistive inorganic semiconductors, called photoinduced current transient spectroscopy (PICTS) on lead bromide 2D-like ((PEA)₂PbBr₄) and standard "3D" (MAPbBr₃) MHP single crystals. We present two conceptually different outcomes of the PICTS measurements, distinguishing the different electronic and ionic contributions to the photocurrents based on the different ion drift of the two materials. Our experiments unveil deep level trap states on the 2D, "ion-frozen" (PEA)₂PbBr₄ and set new boundaries for the applicability of PICTS on 3D MHPs.