Undoped SnO2 as a Support for Ni Species to Boost Oxygen Generation through Alkaline Water Electrolysis

Nanostructured electroless Ni deposited SnO2 for solar hydrogen production

Herein, Ni-decorated SnO2 (Ni@SnO2) nanostructures have been synthesized using SnO2 as a matrix via a simple electroless deposition method for the generation of hydrogen, a potent near-future fuel. XRD analysis confirmed the generation of rutile SnO2 in Ni@SnO2. FESEM and FETEM imaging exhibited the formation of SnO2 nanoparticles with a size of 10-50 nm, which are deposited with Ni nanoparticles (5-7 nm) and intermittent films (thickness 1-2 nm). The associated EDS elemental mapping validated Ni deposition on the surface of the SnO2 nanoparticles, further supplemented by FTIR, Raman and XPS analysis. Slight red shifts in the band gaps of the Ni@SnO2 nanostructures (in the range of 3.53-3.65 eV) compared to the pristine SnO2 nanoparticles (3.72 eV) were observed. Also, intensity quenching of the band gap and associated defect peaks were observed in PL analysis. The Ni@SnO2 nanostructures were used as photocatalysts and exhibited proficient hydrogen evolution. Among the samples, the 0.3 wt% Ni@SnO2 nanostructures showed the greatest hydrogen evolution, i.e., ∼50 μmol g-1 h-1 under visible light irradiation versus pristine SnO2 (8.5 μmol g-1 h-1) owing to the enhanced density of active sites and effective charge separation. It is noteworthy that the hydrogen evolution is much better as compared to earlier reports of Pt-doped-SnO2 based materials.

Tuning the Local Environment of Pt Species at CNT@MO2-x (M = Sn and Ce) Heterointerfaces for Boosted Alkaline Hydrogen Evolution

As the most promising hydrogen evolution reaction (HER) electrocatalysts, platinum (Pt)-based catalysts still struggle with sluggish kinetics and expensive costs in alkaline media. Herein, we accelerate the alkaline hydrogen evolution kinetics by optimizing the local environment of Pt species and metal oxide heterointerfaces. The well-dispersed PtRu bimetallic clusters with adjacent MO2-x (M = Sn and Ce) on carbon nanotubes (PtRu/CNT@MO2-x) are demonstrated to be a potential electrocatalyst for alkaline HER, exhibiting an overpotential of only 75 mV at 100 mA cm-2 in 1 M KOH. The excellent mass activity of 12.3 mA μg-1Pt+Ru and specific activity of 32.0 mA cm-2ECSA at an overpotential of 70 mV are 56 and 64 times higher than those of commercial Pt/C. Experimental and theoretical investigations reveal that the heterointerfaces between Pt clusters and MO2-x can simultaneously promote H2O adsorption and activation, while the modification with Ru further optimizes H adsorption and H2O dissociation energy barriers. Then, the matching kinetics between the accelerated elementary steps achieved superb hydrogen generation in alkaline media. This work provides new insight into catalytic local environment design to simultaneously optimize the elementary steps for obtaining ideal alkaline HER performance.

Metal-Acid Bifunctional Catalysts toward Tandem Reaction: One-Step Hydroalkylation of Benzene to Cyclohexylbenzene

The one-step hydroalkylation of benzene to cyclohexylbenzene (CHB) is a technically challenging and economically interesting reaction with great industrial importance, where bifunctional catalysts play a crucial role in such a tandem reaction. In this work, we report H₃PW₁₂O₄₀ (HPW) modified Ni nanoparticles (NPs) supported on mixed metal oxides (Ni/MMOs), which are featured by HPW species localized on the surface of Ni NPs (denoted as HPW-Ni/MMOs). The optimal catalyst (0.3HPW-Ni/MMOs) exhibits a satisfactory catalytic performance toward benzene hydroalkylation to CHB with a CHB yield of up to 41.2%, which is the highest standard among previously reported catalysts to date. A combination investigation based on HR-TEM, XPS, XANES, and in situ FT-IR verified the electron transfer from the W atom to the adjacent Ni atom, which facilitated the formation and desorption of cyclohexene (CHE) from Ni followed by the alkylation reaction of benzene and CHE at the interfacial Brønsted (B) acid sites of HPW, accounting for the significantly enhanced catalytic behavior. It is proposed that the HPW-Ni interface structure in xHPW-Ni/MMOs samples provides unique adsorption sites for benzene and CHE with a moderate adsorption strength, which serve as the intrinsic active center for this reaction: the Ni site promotes the hydrogenation of benzene to CHE, while the B acid site in HPW facilitates the alkylation of CHE and benzene to produce CHB. This work provides a fundamental understanding of the metal-acid synergistic catalysis toward the hydroalkylation reaction, which can be extended to the design and preparation of high-performance catalysts used in tandem reactions.

Layered Porous Graphitic Carbon Nitride Stabilized Effective Co2SnO4 Inverse Spinel as a Bifunctional Electrocatalyst for Overall Water Splitting

Developing an efficient, low-cost, and non-noble metal oxide-based nanohybrid material for overall water splitting is a highly desirable approach to promote clean energy harnessing and to minimize environmental issues. Accordingly, we proposed an interfacial engineering approach to construct layered porous graphitic carbon nitride (g-C₃N₄)-stabilized Co₂SnO₄ inverse spinel nanohybrid materials as highly active bifunctional electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in an alkaline medium. Here, a Co₂SnO₄/g-C₃N₄ nanohybrid with a layered porous g-C₃N₄ stabilized cubelike inverse spinel has been synthesized with an enhanced surface area via a simple one-pot hydrothermal method. Besides, detailed structural and morphological characterizations were carried out using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field emission-scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HR-TEM), Fourier transform infrared (FT-IR), and Brunauer-Emmett-Teller (BET) analysis. Briefly, XPS analysis has revealed the existence of a strong coupling bond at the interface between a definite proportion of g-C₃N₄ nanosheets and the inverse spinel, which act as an electron transport channel to explore the exceptional performances for HER and OER. Compared to the Co₂SnO₄ inverse spinel lattice or g-C₃N₄ nanosheets, the prepared Co₂SnO₄/g-C₃N₄ nanohybrid-loaded 316 SSL mesh electrode showed excellent and stable electrocatalytic performances with very low overpotentials of 41 mV for HER and 260 mV for OER to reach the current density of 10 mA cm^-2. To understand the electrocatalytic phenomena, the faradic efficiency was calculated for the prepared bifunctional electrocatalyst as 96%, which effectively would favor water electrolysis. Accordingly, the Co₂SnO₄/g-C₃N₄ nanohybrid-loaded electrodes were constructed, and the minimum cell voltage was found to be 1.52 V to reach the current density of 10 mA cm^-2, which is comparable to the standard RuO₂∥Pt/C in two-electrode systems. Thus, the developed nanohybrid-based electrocatalyst could be an alternative to noble metal-centered systems for highly efficient overall water splitting.

Boosting room-temperature ppb-level NO2 sensing over reduced graphene oxide by co-decoration of α-Fe2O3 and SnO2 nanocrystals

As promising sensing materials, reduced graphene oxide (RGO)-based nanomaterials have drawn considerable attention in the fields of gas monitoring owing to their low operating temperature. However, constructing RGO-based room-temperature gas sensors possessing ppb-level limit of detection with high sensitivity remains challenging. In this work, a series of highly sensitive NO₂ sensors were fabricated using α-Fe₂O₃ and SnO₂ co-decorated RGO hybrids (designated as α-Fe₂O₃/SnO₂-RGO) as sensing materials. They were rationally synthesized by a one-pot hydrothermal method. Compared to SnO₂ modified RGO hybrids (SnO₂-RGO with bandgap of 3.88 eV), the bandgap energy of α-Fe₂O₃/SnO₂-RGO hybrids (3.53 eV) was reduced by adding α-Fe₂O_3; the narrower bandgap facilitated the sensing materials to release more electrons and form more oxygen ions at room temperature. Besides, the high carrier migration of RGO, which served as continuous phase, identical structure with ultrasmall particle size of α-Fe₂O₃ and SnO₂ (about 3-6 nm), and abundant chemisorbed oxygen species on the surface (20.8%) of the sensing materials, as well as their suitable bandgap (3.53 eV) in the sensing materials, significantly improved NO₂ response at room temperature. Among the sensors fabricated, α-Fe₂O₃/SnO₂-RGO-15-based NO₂ sensor had the highest response of 7.4 with a short response time of 59 s towards 1 ppm NO₂; it could even reach a response of 2.6 towards 100 ppb NO₂. Notably, α-Fe₂O₃/SnO₂-RGO-15 sample has excellent capability to recognize NO₂, where the response value (7.4) towards 1 ppm NO₂ is about 7 times higher than that of 100 ppm ammonia and common volatile organic compounds (formaldehyde, toluene, ethanol and acetone). Such NO₂ sensor has superior repeatability with negligible response deviation towards 1 ppm NO₂ for four reversible cycles. This makes it to have a great potential application in the field of NO₂ detection.

Metal-organic framework derived ultralow-loading platinum-copper catalyst: a highly active and durable bifunctional electrocatalyst for oxygen-reduction and evolution reactions

Electrocatalysts with high active oxygen reduction (ORR) and oxygen evolution reaction (OER) activities are key factors in renewable energy technologies. Unlike common strategies for adjusting the proportion of metal centers in a multi-metal organic framework (MOF), herein, we designed and synthesized bifunctional electrocatalysts using cetyltrimethylammonium bromide (CTAB)-capped ultra-low content platinum (Pt) (≤0.5 wt.% Pt) and copper (Cu) nanoparticles and doped on the surface of zinc-based MOF (Zn-MOF-74) and calcinated at 900 °C. According to the electrochemical activity, the Pt/Cu/NPC-900 exhibits superior catalytic activities towards both the ORR with the onset (E₀) and half-wave (E_1/2) potentials were 1.0 V and 0.89 V versus RHE, respectively, and OER (E_o = 1.48 V versus RHE and overpotential (η) = 0.265 V versus RHE) in an alkaline electrolyte at ambient temperature. Also, Pt/Cu/NPC-900 catalyzes through a 4^-electron process and exhibits superior stability. Such insightful findings, as well as a newly developed approach, provides rational design and synthesis of an economical and efficient strategy for bifunctional electrocatalyst development.

VAlPOs as Efficient Catalysts for Glycerol Conversion to Methanol

The catalytic activity of a series of vanadium aluminophosphates catalysts prepared by sol-gel method followed by combustion of the obtained gel was evaluated in glycerol conversion towards methanol. The materials were characterized by several techniques such as X-ray diffraction (XRD), UV-vis, Fourier-transform infrared (FTIR), Raman and X-ray photoelectron (XPS) spectroscopies. The amount of vanadium incorporated in aluminophosphates framework played an important role in the catalytic activity, while in the products distribution the key role is played by the vanadium oxidation state on the surface. The sample that contains a large amount of V4+ has the highest selectivity towards methanol. On the sample with the lowest vanadium loading the oxidation path to dihydroxyacetone is predominant. The catalyst with higher content of tetrahedral isolated vanadium species, such V5APO, is less active in breaking the C–C bonds in the glycerol molecule than the one containing polymeric species.