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Polymeric carbon nitride (CN) has emerged as a promising photoanodic material in water‐splitting photoelectrochemical cells (PEC). However, the current deposition methods of CN layers on substrates usually include a long heating process at 500−550 °C, which might cause sublimation or decomposition of the CN monomers and destruction of the substrate, leading to a nonuniform CN film. Herein, a simple, fast, and scalable energy‐economic procedure to synthesize homogenous CN films is introduced. The predesigned CN monomers film is subjected for several minutes to higher temperatures than the standard calcination procedure. The short heating process allows the formation of a uniform CN layer, with excellent contact with the substrate and good activity as a photoanode in PEC. The optimal CN photoanode reaches photocurrent densities of ≈200 μA cm−2 at 1.23 versus reversible hydrogen electrode in neutral and acidic solutions and 120 μA cm−2 in a basic solution. [ABSTRACT FROM AUTHOR]

The prevailing view about molecular catalysts is that the central metal ion is responsible for the reaction mechanism and selectivity, whereas the ligands mainly affect the reaction kinetics. Here, we question this paradigm and show that ligands have a dramatic influence on the selectivity of the product. We show how even a seemingly small change in ligand isomerization sharply alters the selectivity of the well‐researched oxygen reduction reaction (ORR) Co phthalocyanine catalyst from an indirect 2e− to a direct 4e− pathway. Detailed analysis reveals that intramolecular hydrogen‐bond interactions in the ligand activate the catalytic Co, directing the oxygen binding and thus deciding the final product. The resulting catalyst is the first example of a Co‐based molecular catalyst catalyzing a direct 4e− ORR via ligand isomerization, for which it shows an activity close to the benchmark Pt in an actual H2−O2 fuel cell. The effect of the ligand isomerism is demonstrated with different central metal ions, thus highlighting the generalizability of the findings and their potential to open new possibilities in the design of molecular catalysts. [ABSTRACT FROM AUTHOR]

Controlling the properties of a polymeric carbon nitride (CN) layer during its in situ growth on a conductive substrate, including its directionality, morphology, specific surface area, and defects, is challenging because of the high temperature of the reaction and the substrate properties. Here, we report the growth of defect-rich, porous 1D CN with enhanced optical properties and photocatalytic activity by utilizing sophisticated supramolecular assemblies composed of melamine and HCl as starting precursors. The supramolecular assembly composition directs the 1D growth, and the presence of protonated amines in the precursor leads to partial condensation and defect generation. The 1D configuration, high specific surface area, and abundance of defects of the photoanode result in high photoelectrochemical activity for water and benzylamine oxidation. The new design of the CN photoanode leads to very low overpotential, good photocurrent density of 183 ± 8 μA cm−2 at 1.23 V vs. reversible hydrogen electrode (RHE), with an incident photon to current efficiency (IPCE) of up to 10.5% and enhanced stability (retaining ∼62% activity) for 10 h. Moreover, the conversion of benzylamine into benzaldehyde and imine N-benzylideneaniline in the presence of O2 reaches 56% compared to 16% for the reference CN photoanode. [ABSTRACT FROM AUTHOR]

Polymeric carbon nitrides (CN) have gained significant interest as photoanodes in photoelectrochemical cells (PEC). A widely researched approach for synthesizing CN films with controlled optical and photoelectrochemical properties relies on using supramolecular assemblies as the precursors for thermal polymerization over a transparent conductive substrate. However, the formation of supramolecular assemblies is highly dependent on the temperature and solubility in a given solvent, limiting the full potential of this method. Moreover, the intercalation of metal ions is challenging due to the use of polar solvents. Here, this study shows a new way of synthesizing supramolecular assemblies with metal ions using a solvothermal approach. The solvent, monomer composition, salt quantity, reaction temperature, and film thickness are varied in this study. As a result, well‐attached, uniform CN films with good optoelectronic properties are achieved. The synthesized photoactive CN films exhibit very low onset potentials and reach ≈0.13, ≈0.15, and 0.30 ± 0.01 mA cm−2 photocurrents in 0.1 m phosphate buffer (neutral) solution, 0.1 m KOH(aq) (basic) solution, and 0.1 m KOH solution containing 10 vol.% triethanolamine as the hole scavenger, respectively. [ABSTRACT FROM AUTHOR]

Doped and alloyed transition metal-oxides (TMOs) attract vast attention owing to their tunable electronic properties (e.g., conductivity, band gap, and optical absorption), making them appealing for many (photo)-electronic, chromic, and green energy applications. Dual-functional materials combining electrochromic (EC) and energy storage (e.g., supercapacitor, SC) applications are of interest as they can store energy while shading the light transmission through a window or give off a visual signal of their current energy storage state by a color change. Pure tungsten-oxides exhibit distinctive EC properties but attain low energy density compared to other TMOs (e.g., MoO3 and V2O5). The coloration efficiency and energy density can be enhanced by controlling the morphology, size, and composition of the nanoscale TMOs that constitute the active EC film. Thus far, most EC-SC works showed a trade-off between increased areal capacitance and a decrease in the coloration efficiency or transmittance; the improved EC-SC properties for doped or alloyed metal-oxides were related mostly to the small grain size or to structural distortion caused by the added cation, exhibiting more active sites. Herein, we demonstrate a straightforward and facile synthesis of crystalline Mo/V-alloyed tungsten-oxide ultrathin nanowires (uNWs). We investigated the growth mechanism and succeeded in preserving the crystallinity up to 25% (atomic) alloying. The additional properties (compared to unmodified tungsten-oxide) of the alloyed uNWs, such as absorbance peaks, lead to improved specific capacitance while preserving the high coloration efficiency of uNW W–O, and in the case of W–Mo–O, a better coloration efficiency is measured. [ABSTRACT FROM AUTHOR]

The electrochemical properties of spinel ferrites have been studied since the 1970s after the pioneering discovery of water electrolysis by using TiO2 as the photoanode in a photoelectrochemical cell. Several approaches have been developed to fabricate ferrites of different sizes and shapes but most of these methods suffer from several disadvantages, such as the difficulty to produce the ferrite in a thin layer form or on top of another (pre‐prepared) structure as a second layer. Moreover, the formation process requires calcination at high temperatures, and the electrode fabrication requires an additional assembly method. Herein, a CdFe2O4 ferrite was formed via chemical vapor deposition of a single‐source precursor directly on a hematite structure followed by an annealing process. This thermal treatment simultaneously achieves both activation of the hematite and the formation of CdFe2O4. Three different iron oxide (rectangular, nanobelt, and mesoporous) structures were examined as photoanode electrodes. The maximum current at 1.65 V vs. RHE of the mesoporous film was more than two times higher than the rectangular and the nanobelt films. Therefore, iron oxide with mesoporous structures was used to form the hybrid structure of α‐Fe2O3−CdFe2O4. The hybrid structure presents stable and high photocurrent density (about 20 % enhancement in the measured maximum current density at 1.65 V vs. RHE). [ABSTRACT FROM AUTHOR]

The photoelectrochemical oxidation of organic molecules into valuable chemicals is a promising technology, but its development is hampered by the poor stability of photoanodic materials in aqueous solutions, low faradaic efficiency, low product selectivity, and a narrow working pH range. Here, we demonstrate the synthesis of value-added aldehydes and carboxylic acids with clean hydrogen (H2) production in water using a photoelectrochemical cell based solely on polymeric carbon nitride (CN) as the photoanode. Isotope labeling measurements and DFT calculations reveal a preferential adsorption of benzyl alcohol and molecular oxygen to the CN layer, enabling fast proton abstraction and oxygen reduction, which leads to the synthesis of an aldehyde at the first step. Further oxidation affords the corresponding acid. The CN photoanode exhibits excellent stability (>40 h) and activity for the oxidation of a wide range of substituted benzyl alcohols with high yield, selectivity (up to 99%), and faradaic efficiency (>90%). [ABSTRACT FROM AUTHOR]