Defect-rich cobalt pyrophosphate hybrids decorated Cd0.5Zn0.5S for efficient photocatalytic hydrogen evolution: Defect and interface engineering

Construction of a transition-metal sulfide heterojunction photocatalyst driven by a built-in electric field for efficient hydrogen evolution under visible light

Photocatalytic H2 evolution is of prime importance in the energy crisis and in lessening environmental pollution. Adopting a single semiconductor as a photocatalyst remains a formidable challenge. However, the construction of an S-scheme heterojunction is a promising method for efficient water splitting. In this work, CdS nanoparticles were loaded onto NiS nanosheets to form CdS/NiS nanocomposites using hollow Ni(OH)2 as a precursor. The differences in the Fermi energy levels between the two components of CdS and NiS resulted in the formation of a built-in electric field in the nanocomposite. Density functional theory (DFT) calculations reveal that the S-scheme charge transfer driven by the built-in electric field can accelerate the effective separation of photogenerated carriers, which is conducive to efficient photocatalytic hydrogen evolution. The hydrogen evolution rate of the optimized photocatalyst is 39.68 mmol·g-1 h-1, which is 6.69 times that of CdS under visible light. This work provides a novel strategy to construct effective photocatalysts to relieve the environmental and energy crisis.

Dinitrogen Reduction Coupled with Methanol Oxidation for Low Overpotential Electrochemical NH3 Synthesis Over Cobalt Pyrophosphate as Bifunctional Catalyst

Electrochemical dinitrogen (N₂ ) reduction to ammonia (NH₃ ) coupled with methanol electro-oxidation is presented in the current work. Here, methanol oxidation reaction (MOR) is proposed as an alternative anode reaction to oxygen evolution reaction (OER) to accomplish electrons-induced reduction of N₂ to NH₃ at cathode and oxidation of methanol at anode in alkaline media thereby reducing the overall cell voltage for ammonia production. Cobalt pyrophosphate micro-flowers assembled by nanosheets are synthesized via a surfactant-assisted sonochemical approach. By virtue of structural and morphological advantages, the maximum Faradaic efficiency of 43.37% and NH₃ yield rate of 159.6 µg h^-1 mg_ca ^-1 is achieved at a potential of -0.2 V versus RHE. The proposed catalyst is shown to also exhibit a very high activity (100 mA mg^-1 at 1.48 V), durability (2 h) and production of value-added formic acid at anode (2.78 µmol h^-1 mg_cat ^-1 and F.E. of 59.2%). The overall NH₃ synthesis is achieved at a reduced cell voltage of 1.6 V (200 mV less than NRR-OER coupled NH₃ synthesis) when OER at anode is replaced with MOR and a high NH₃ yield rate of 95.2 µg h^-1 mg_cat ^-1 and HCOOH formation rate of 2.53 µmol h^-1 mg^-1 are witnessed under full-cell conditions.

Electrochemically Reconstructed Vanadic Oxide-Doped Cobalt Pyrophosphate as an Electrocatalyst for the Oxygen Evolution Reaction

More and more attention has been paid to the development of the efficient electrocatalysts for the oxygen evolution reaction (OER). Herein, a porous vanadic oxide-doped cobalt pyrophosphate electrocatalyst, namely V₂O₅-Co₂P₂O₇, was exploited by using the electrochemical reconstruction method in the alkaline electrolyte and selecting a cobalt vanadium phosphate Co(H₂O)₄(VOPO₄)₂ as a precursor. The reconstructed vanadic oxide-doped cobalt pyrophosphate catalyst V₂O₅-Co₂P₂O₇ exhibited efficient electrocatalytic activity for the OER in 1.0 M KOH, requiring a low overpotential of 199 mV at 10 mA cm^-2, compared to the reported pyrophosphate electrocatalysts. The porous morphology and doping of vanadic oxide after electrochemical reconstruction were beneficial to enhance the electrocatalytic performance for the OER, through improving the surface area to bring in more accessibly active sites and regulating the electronic structures. The results provided a promising strategy to prepare the pyrophosphate electrocatalysts and improve the performance of the OER catalyst.

Incorporating Ni-Polyoxometalate into the S-Scheme Heterojunction to Accelerate Charge Separation and Resist Photocorrosion for Promoting Photocatalytic Activity and Stability

The emerging polyoxometalate (POM) nanomaterials are transition metal oxygen anion clusters with d⁰ electronic configurations, which could be attractive and potential photocatalysts. Hence, a nickel (Ni)-substituted polyoxometalate K₆Na₄[Ni₄(H₂O)₂(PW₉O₃₄)₂]·32H₂O (Ni₄POM)-incorporating step (S)-scheme heterojunction was developed to promote photocatalytic activity and stability in H₂ and H₂O₂ production. The multielectron transfer through variable valence metal centers in Ni₄POM would facilitate the recombination of invalid charges through the S-scheme pathway. Moreover, incorporating Ni₄POM into the S-scheme heterojunction can broaden the light absorption range and meanwhile lead to resistance to photocorrosion to promote the optical and chemical stability of Cd_0.5Zn_0.5S (CZS). The optimized CZSNi-70 exhibited a H₂ evolution rate of 42.32 mmol g^-1 h^-1 under visible-light irradiation with an apparent quantum yield of 32.27% at 420 nm and a H₂O₂ production rate of 295.4 μmol L^-1 h^-1 under 420 nm light-emitting diode irradiation. This work can provide a new view for the development of transition metal-substituted POM-based stable and efficient S-scheme photocatalysts.

Microfluidic assisted low-temperature and speedy synthesis of TiO2/ZnO/GOx with bio/photo active cites for amoxicillin degradation

For the first time, a bio-photo-catalyst is synthesized in a microfluidic platform. The microchannel, which is wall-coated by in situ synthesized bio-photo-catalyst is used as an opto-fluidic reactor for amoxicillin degradation. Analyses including SEM, XRD, FTIR, Raman, UV–Vis spectra, and DLS have been used to characterize samples. The structure and morphology of TiO2 in microfluidic assisted synthesis are studied at 70–120 °C. The results show that both single-crystalline anatase sample and two-phase samples of anatase and rutile can be attained. According to SEM images, the smallest size and the narrowest particle size distribution (0.86 nm $$\pm \hspace{0.17em}0.14$$ ± 0.14 ) is achieved by synthesis at 70 °C. Elemental mapping of Ti shows a uniform coating layer on inner walls. Raman signals besides the primary amines in FTIR results show the biological activity of the cross-linked Glucose oxidase (GOx), which is aimed for situ generation of H2O2. FTIR comparison of bulk and spiral microfluidic synthesized ZnO indicates identical bonds. SEM-coupled with performance experimentation reveal that by regulating the flowrate of spiral micromixer for ZnCl2 at 25 µl/min and NaOH at 50 µl/min, the narrowest size distribution and best the bio-photo-catalytic performance of ZnO nanoparticles is observed.

Construction of novel noble-metal-free MoP/CdIn2S4 heterojunction photocatalysts: Effective carrier separation, accelerating dynamically H2 release and increased active sites for enhanced photocatalytic H2 evolution

Developing novel photocatalysts with high performance is significant for the practical application of photocatalytic H₂ production. Herein, novel and noble-metal-free heterojunction photocatalysts contained CdIn₂S₄ nanoparticles and bulk MoP were prepared. The H₂-production rate of optimal MoP/CdIn₂S₄ (MPCIS) composites achieved at 286.10 μmol g^-1h^-1, which was nearly 2.2 times that of CdIn₂S₄-1 %Pt (130.51 μmol g^-1h^-1). Electrochemical and PL results displayed that MoP cocatalyst could vastly boost the carrier separation efficiency of CdIn₂S₄. The high carrier separation efficiency maybe put down to the Fermi level rearrangement between MoP and CdIn₂S₄. The linear sweep voltammograms tests showed that, compared to CdIn₂S₄, CdIn₂S₄ with 30 %MoP (30MPCIS) has smaller Tafel slopes and lower H₂ evolution overpotentials, which contributed to facilitate H₂ release in kinetics. The 30MPCIS composites possess higher C_dl value and MoP has Pt-like electronic structure, so that MoP could offer abundant surface reaction sites of MPCIS composites for HER. Aforementioned results demonstrate that MoP may have great potential in replacing precious metal Pt for photocatalytic H₂ production. It is expected that this study can provide new insights into developing the novel sulfide-based heterojunction photocatalysts with MoP as cocatalyst for resultful photocatalytic H₂ generation.

Nickel phosphonate-derived Ni2P@N-doped carbon co-catalyst with built-in electron-bridge for boosting the photocatalytic hydrogen evolution

To construct photocatalytic systems that can efficiently convert solar energy to hydrogen energy, numerous studies have been focused on transition metal phosphides (TMPs) co-catalysts, which display low overpotential and cost...