Bismuth Vanadate with Electrostatically Anchored 3D Carbon Nitride Nano-networks as Efficient Photoanodes for Water Oxidation

Efficient UV-Vis-NIR Responsive CO2 Reduction Photocatalyst with Black Pinecone-Shaped Carbon Nitride Loaded with Lanthanum Oxide

Photothermal catalysis combines the advantages of photocatalysis and thermal activation, which provides a new research angle for CO2 catalytic reduction. In this study, Black carbon nitride with a three-dimensional (3D) pinecone-shaped structure (BPCN) was prepared by a simple solvothermal method using melamine as a precursor without the aid of a template. Lanthanum oxide doping on the BPCN catalysts (BPCN-La) was achieved by ultrasonic impregnation. This unique pinecone-shaped structure consists of self-assembled and interlaced carbon nitride rods (by SEM). The lanthanum element was distributed on the surface of the CN framework in the form of La2O3 (by XPS). The chemical structures of the samples were characterized by solid-state 13C nuclear magnetic resonance (13C NMR) and elaborated by density functional theory (DFT) analysis. This black carbon nitride expanded the light absorption band edge into the near-infrared (NIR) (300-1400 nm, by UV-vis absorption spectra) and had excellent photothermal conversion activity. La atom doping can significantly boost photogenerated electron excitation (by photocurrent test) and promote carrier separation and transfer (by PL). Upon incorporation of La atoms into BPCN, the highest occupied molecular orbital (HOMO) orbital is more concentrated on the oxygen atoms of La2O3. BPCN-La considerably narrowed the band gap width, exhibited an exceptional photothermal effect, and provided a large surface area, which significantly enhanced the photocatalytic reduction of CO2 reactions. The yields of CO reached 58.2 and 104.9 μmol·h-1·g-1 for BPCN and BPCN-La, respectively, with GCN as the control (6.3 μmol·h-1·g-1). Theoretical reaction pathways and selectivity for the photoreduction of CO2 on BPCN and BPCN-La were studied by DFT simulation. This work provides a new vision for the design of photothermal synergistic without extra-thermal input and full spectral response photocatalysts with high efficiency.

Engineering Nanostructure-Interface of Photoanode Materials Toward Photoelectrochemical Water Oxidation

Photoelectrochemical (PEC) water oxidation based on semiconductor materials plays an important role in the production of clean fuel and value-added chemicals. Nanostructure-interface engineering has proven to be an effective way to construct highly efficient PEC water oxidation photoanodes with good light capture, carrier transport, and water oxidation kinetics. However, from theoretical and application perspectives, the relationship between the nanostructure and interface of photoanode materials and their PEC performance remains unclear. In this review, the PEC water oxidation reaction mechanism and evaluation criteria are briefly presented. The theoretical basis and research status of the nanostructure-interface engineering on constructing high-performance PEC water oxidation photoanodes are summarized and discussed. Finally, the current challenges and the future opportunities of nanostructure-interface engineering for the PEC reactions are pointed out.

BiNV bond: A hole-transfer bridge for high-efficient separation and transfer of carriers

Addressing the inherent holes transport limitation of BiVO₄ photoanode is crucial to achieve efficient photoelectrochemical (PEC) water splitting. The construction of the hole-transfer bridge between co-catalysts and BiVO₄ photoanode could be an effective way to overcome sluggish hole-transfer kinetics of BiVO₄ photoanode. Herein, C_xN_y/BiVO₄ photoanode was prepared by coupling carbon nitride hydrogel (CNH) containing unsaturated N on the BiVO₄ photoanode during annealing. C_xN_y/BiVO₄ photoanode exhibited excellent PEC performance and stability. Photoelectrochemical tests proved that the coupling of C_xN_y accelerated holes transfer and enhanced oxygen evolution kinetics. X-ray photoelectron spectroscopy (XPS) and theoretical calculations confirmed the existence of the BiNV bond between BiVO₄ photoanode and C_xN_y, which could serve as the hole-transfer bridge to significantly accelerate separation and transfer of carriers driven by the interfacial electric field. Moreover, it was found that the coupling of C_xN_y effectively inhibited the dissociation of metal ions through changing their coordination environment, resulting in the excellent stability of C_xN_y/BiVO₄ photoanode. This result provides unique insights into vital roles of the interfacial structure, which might have a significant impact on the construction of PEC devices.

Constructing electron transfer pathways and active centers over W18O49 nanowires by doping Fe3+ and incorporating g-C3N5 for enhanced photocatalytic nitrogen fixation

A compound constructed from fluffy and porous g-C₃N₅ with OV-rich Fe-W₁₈O₄₉ was employed in the photocatalytic nitrogen fixation. The formation rate of ammonia reached 131.6 μmol g⁻¹ h⁻¹ when Fe-W₁₈O₄₉/g-C₃N₅ was employed as the catalyst.

Photoelectrochemical Solar Water Splitting: The Role of the Carbon Nanomaterials in Bismuth Vanadate Composite Photoanodes toward Efficient Charge Separation and Transport

Photoelectrochemical performance of bismuth vanadate (BiVO₄) photoanode is limited by poor charge separation and transport properties. The roles of carbon nanotube, reduced graphene oxide, or graphitic carbon nitride in BiVO₄ composite photoanode were investigated toward enhancing light absorption and reducing overall impedance during photoelectrochemical water oxidation process. X-ray diffraction and Tauc analysis showed that BiVO₄ retains its monoclinic phase, n-type semiconductor nature, and band gap in all carbon nanomaterials-incorporated composite photoanodes. It was observed that the carbon nanomaterials incorporation in BiVO₄ film increases its surface porosity, ultimately leading to enhanced light absorption. The BiVO₄ photoanode with reduced graphene oxide and graphitic carbon nitride showed same bulk charge separation efficiency, whereas the latter showed better charge transfer. It was found that the graphitic carbon nitride formed composite with BiVO₄ to provide enhanced light absorption efficiency, i.e., 89% in 350-505 nm range. The BiVO₄ with graphitic carbon nitride photoanode showed the best performance with a photocurrent of 2.2 mA cm^-2, charge separation efficiency of 67%, and photocurrent of 4.0 mA cm^-2 with cobalt-phosphate surface catalyst at 1.23 V_RHE for water oxidation under 1 sun illumination. The Mott-Schottky and impedance measurements confirmed the shift of conduction band position toward hydrogen reduction potential and reduction in film resistance, respectively, with carbon nanomaterials addition, and the shift was most significant for graphitic carbon nitride. It is concluded that by concomitant formation of junction during photoanode fabrication between carbon nanomaterials, BiVO₄, and fluorine-doped tin oxide glass substrate, better charge separation, transport, and light absorption can be achieved.

Dual Quantum Dot-Decorated Bismuth Vanadate Photoanodes for Highly Efficient Solar Water Oxidation

Photo-induced charge separation and photon absorption play important roles in determining the performance of the photoelectrocatalytic water splitting process. In this work, we utilize dual quantum dots (QDs), consisting of BiVO₄ and carbon, to fabricate a hybrid homojunction-based BiVO₄ photoanode for efficient and stable solar water oxidation. Formation of homojunctions, by decorating as-prepared BiVO₄ substrate with BiVO₄ QDs, enhances the charge separation efficiency by 1.3 times. This enhancement originates from lattice match, which benefits charge transfer across the interface. Furthermore, the use of carbon QDs as a stable photosensitizer effectively extends the photon absorption limit from 520 nm to over 700 nm, yielding an incident photon-to-electron conversion efficiency of 6.0 %, even at 600 nm at 1.23 V versus RHE. Finally, a remarkable photocurrent density of 6.1 mA cm^-2 at 1.23 V was recorded after depositing FeOOH/NiOOH as cocatalysts, thereby, reaching 82 % of the theoretical efficiency for BiVO₄ .

Versatile Synthesis of Pd and Cu Co-Doped Porous Carbon Nitride Nanowires for Catalytic CO Oxidation Reaction

Developing efficient catalyst for CO oxidation at low-temperature is crucial in various industrial and environmental remediation applications. Herein, we present a versatile approach for controlled synthesis of carbon nitride nanowires (CN NWs) doped with palladium and copper (Pd/Cu/CN NWs) for CO oxidation reactions. This is based on the polymerization of melamine by nitric acid in the presence of metal-precursors followed by annealing under nitrogen. This intriguingly drove the formation of well-defined, one-dimensional nanowires architecture with a high surface area (120 m2 g−1) and doped atomically with Pd and Cu. The newly-designed Pd/Cu/CN NWs fully converted CO to CO2 at 149 °C, that was substantially more active than that of Pd/CN NWs (283 °C) and Cu/CN NWs (329 °C). Moreover, Pd/Cu/CN NWs fully reserved their initial CO oxidation activity after 20 h. This is mainly attributed to the combination between the unique catalytic properties of Pd/Cu and outstanding physicochemical properties of CN NWs, which tune the adsorption energies of CO reactant and reaction product during the CO oxidation reaction. The as-developed method may open new frontiers on using CN NWs supported various noble metals for CO oxidation reaction.