Electrochemical Polymerization Provides a Function-Integrated System for Water Oxidation

Selective Valorization of Glycerol to Formic Acid on a BiVO4 Photoanode through NiFe Phenolic Networks

The integration of the glycerol oxidation reaction (GOR) with the hydrogen evolution reaction in photoelectrochemical (PEC) cells is a desirable alternative to PEC water splitting since a large quantity of glycerol is easily accessible as the byproduct from the biodiesel industry. However, the PEC valorization of glycerol to the value-added products suffers from low Faradaic efficiency and selectivity, especially in acidic conditions, which is beneficial for hydrogen production. Herein, by loading bismuth vanadate (BVO) with a robust catalyst composed of phenolic ligands (tannic acid) coordinated with Ni and Fe ions (TANF), we demonstrate a modified BVO/TANF photoanode for the GOR with a remarkable Faradaic efficiency of over 94% to value-added molecules in a 0.1 M Na₂SO₄/H₂SO₄ (pH = 2) electrolyte. The BVO/TANF photoanode achieved a high photocurrent of 5.26 mA·cm^-2 at 1.23 V versus reversible hydrogen electrode under 100 mW/cm² white light irradiation for formic acid production with 85% selectivity, equivalent to 573 mmol/(m²·h). Transient photocurrent and transient photovoltage techniques and electrochemical impedance spectroscopy along with intensity-modulated photocurrent spectroscopy indicated that the TANF catalyst could accelerate hole transfer kinetics and suppress charge recombination. Comprehensive mechanistic investigations reveal that the GOR is initiated by the photogenerated holes of BVO, while the high selectivity to formic acid is attributed to the selective adsorption of primary hydroxyl groups in glycerol on TANF. This study provides a promising avenue for highly efficient and selective formic acid generation from biomass in acid media via PEC cells.

Simultaneous Electrochemical Sensing of Indole-3-Acetic Acid and Salicylic Acid on Poly(L-Proline) Nanoparticles–Carbon Dots–Multiwalled Carbon Nanotubes Composite-Modified Electrode

Sensitive simultaneous electrochemical sensing of phytohormones indole-3-acetic acid and salicylic acid based on a novel poly(L-Proline) nanoparticles–carbon dots composite consisting of multiwalled carbon nanotubes was reported in this study. The poly(L-Proline) nanoparticles–carbon dots composite was facilely prepared by the hydrothermal method, and L-Proline was used as a monomer and carbon source for the preparation of poly(L-Proline) nanoparticles and carbon dots, respectively. Then, the poly(L-Proline) nanoparticles–carbon dots–multiwalled carbon nanotubes composite was prepared by ultrasonic mixing of poly(L-Proline) nanoparticles–carbon dots composite dispersion and multiwalled carbon nanotubes. Scanning electron microscope, transmission electron microscope, Fourier transform infrared spectroscopy, ultraviolet visible spectroscopy, energy dispersive spectroscopy, cyclic voltammetry, electrochemical impedance spectroscopy, and linear sweep voltammetry were used to characterize the properties of the composite. poly(L-Proline) nanoparticles were found to significantly enhance the conductivity and sensing performance of the composite. Under optimal conditions, the composite-modified electrode exhibited a wide linear range from 0.05 to 25 μM for indole-3-acetic acid and from 0.2 to 60 μM for salicylic acid with detection limits of 0.007 μM and 0.1 μM (S/N = 3), respectively. In addition, the proposed sensor was also applied to simultaneously test indole-3-acetic acid and salicylic acid in real leaf samples with satisfactory recovery.

Electropolymerization of Metal Clusters Establishing a Versatile Platform for Enhanced Catalysis Performance

Atomically precise metal clusters are attractive as highly efficient catalysts, but suffer from continuous efficiency deactivation in the catalytic process. Here, we report the development of an efficient strategy that enhances catalytic performance by electropolymerization (EP) of metal clusters into hybrid materials. Based on carbazole ligand protection, three polymerized metal-cluster hybrid materials, namely Poly-Cu₁₄ cba, Poly-Cu₆ Au₆ cbz and Poly-Cu₆ Ag₄ cbz, were prepared. Compared with isolated metal clusters, metal clusters immobilizing on a biscarbazole network after EP significantly improved their electron-transfer ability and long-term recyclability, resulting in higher catalytic performance. As a proof-of-concept, Poly-Cu₁₄ cba was evaluated as an electrocatalyst for reducing nitrate (NO₃ ^- ) to ammonia (NH₃ ), which exhibited ≈4-fold NH₃ yield rate and ≈2-fold Faraday efficiency enhancement compared to that of Cu₁₄ cba with good durability. Similarly, Poly-Cu₆ Au₆ cbz showed 10 times higher photocatalytic efficiency towards chemical warfare simulants degradation than the cluster counterpart.

Carbazole modification of ruthenium bipyridine-dicarboxylate oxygen evolution molecular catalysts

We synthesized new oxygen-evolving molecular Ru(II) catalysts with one or two carbazole moieties on the axial pyridyl ligands, namely [Ru(bda)(cbz-py)(py)] and [Ru(bda)(cbz-py)₂] [C1 and C2; bdaH₂ = 2,2'-bipyridyl-6,6'-dicarboxylic acid, py = pyridine, and cbz-py = 9-(pyridin-4-yl)-9H-carbazole] to investigate the effect of cbz modification on the photophysical and catalytic properties of the well-known molecular catalyst [Ru(bda)(py)₂] (C0). The initial oxygen-evolving catalytic activities of C1 and C2 were higher than that of C0 in both a chemical reaction driven by the strong oxidant (NH₄)₂[Ce(NO₃)₆] (CAN = ceric ammonium nitrate) and photochemical oxidation using a [Ru(bpy)₃]²⁺ (bpy = 2,2'-bipyridine) photosensitizer with Na₂S₂O₈ as the sacrificial oxidant. The higher activities were ascribed to the electron-withdrawing cbz groups, which promoted the radical coupling reaction to form a Ru^IV-O-O-Ru^IV species. A unique oxygen-evolution rate change behaviour was observed for both C1 and C2 in the presence of a large excess of CAN, suggesting the competitive oxidation of the cbz moiety during the chemical oxygen evolution reaction. This work suggests that the cbz modification of an oxygen evolution molecular catalyst is a promising approach for integrating the hole accumulator near the oxygen evolution catalytic centre.

Electrodeposition of Fe-Complexes on Oxide Surfaces for Efficient OER Catalysis

Progress in non-covalent/self-assembled immobilization methods on (photo)electrode materials for molecular catalysts could broaden the scope of attainable systems. While covalent linkage (though considered more stable) necessitates functional groups introduced by means of often cumbersome synthetic procedures, non-covalent assemblies require sufficient propensity of the molecular unit for surface adsorption, thus set less rigorous pre-requisites. Herein, we report efficient electrodeposition (ED) of two Fe(III) complexes prepared with closely related NN’N pincer ligands yielding stable and active ad-layers for the electrocatalysis of the oxygen-evolving reaction (OER). The ED method is based on the utilization of a chloride precursor complex [FeIIICl2(NN’N)], which is dissolved in an organic electrolyte undergoes chloride/aqua ligand exchange upon addition of water. ED provides patchy distribution of a chloride-depleted catalyst layer on indium tin oxide (ITO) and fluorine-doped tin oxide (FTO) surfaces, which can be applied for long periods as OER electrocatalysts. Compared to drop-casting or layering of [FeIIICl2(NN’N)] with Nafion (a commonly used support for molecular electrocatalysts), the surface modification by ED is a material saving and efficient method to immobilize catalysts.