Gibbs Free Energy Of Adsorption Research Articles

Self-Assembled Preparation of Porous Nickel Phosphide Superparticles with Tunable Phase and Porosity for Efficient Hydrogen Evolution.

Self-assembly of colloidal nanoparticles enables the easy building of assembly units into higher-order structures and the bottom-up preparation of functional materials. Nickel phosphides represent an important group of catalysts for hydrogen evolution reaction (HER) from water splitting. In this paper, the preparation of porous nickel phosphide superparticles and their HER efficiencies are reported. Ni and Ni2P nanoparticles are self-assembled into binary superparticles via an oil-in-water emulsion method. After annealing and acid etching, the as-prepared Ni-Ni2P binary superparticles change into porous nickel phosphide superparticles. The porosity and crystalline phase of the superparticles can be tuned by adjusting the ratio of Ni and Ni2P nanoparticles. The resulting porous superparticles are effective in driving HER under acidic conditions, and the modulation of porosity and phase further optimize the electrochemical performance. The prepared Ni3P porous superparticles not only possess a significantly enhanced specific surface area compared to solid Ni-Ni2P superparticles but also exhibit an excellent HER efficiency. The calculations based on the density functional theories show that the (110) crystal facet exhibits a relatively lower Gibbs free energy of hydrogen adsorption. This work provides a self-assembly approach for the construction of porous metal phosphide nanomaterials with tunable crystalline phase and porosity.

A Statistical Physics Approach to Understanding the Adsorption of Methylene Blue onto Cobalt Oxide Nanoparticles.

The production of cobalt oxide nanoparticles and their use in the adsorption of methylene blue (MB) from solution is described in the paper. The X-ray diffraction patterns show that the synthesized cobalt oxide nanoparticles have a crystalline cubic structure. The study of the adsorption of methylene blue onto the cobalt oxide nanoparticles involved determining the contact time and initial concentration of the adsorption of MB on the adsorbent. The kinetics of adsorption were analyzed using two kinetic models (pseudo-first order and pseudo-second order), and the pseudo-second-order model was found to be the most appropriate for describing the behavior of the adsorption. This study indicates that the MLTS (monolayer with the same number of molecules per site) model is the most suitable model for describing methylene blue/cobalt oxide systems, and the parameter values help to further understand the adsorption process with the steric parameters. Indicating that methylene blue is horizontally adsorbed onto the surface of the cobalt oxide, which is bonded to two different receptor sites. Regarding the temperature effect, it was found that the adsorption capacity increased, with the experimental value ranging from 313.7 to 405.3 mg g-1, while the MLTS predicted 313.32 and 408.16 mg g-1. From the thermodynamic functions, high entropy was found around 280 mg L-1 concentration. For all concentrations and temperatures examined, the Gibbs free energy and enthalpy of adsorption were found to be negative and positive, respectively, suggesting that the system is spontaneous and endothermic. According to this study's findings, methylene blue adsorption onto cobalt oxide nanoparticles happens via the creation of a monolayer, in which the same amount of molecules are adsorbed at two distinct locations. The findings shed light on the methylene blue adsorption process onto cobalt oxide nanoparticles, which have a variety of uses, including the remediation of wastewater.

Preparation of Co-W-P-O/NF catalyst with crystalline-amorphous phase structure by electrodeposition and study on its water splitting properties

The development of renewable clean energy is imminent as global warming and environmental pollution become more serious issues today. Hydrogen energy has been widely studied as an ideal green energy source. Among several common hydrogen production methods, hydrogen production by electrolysis of water is considered an efficient, environmentally friendly, and sustainable hydrogen production strategy. Transition metal phosphates have outstanding electrocatalytic conductivity and high catalytic efficiency, thus exhibiting catalytic effects similar to noble metals. To further enhance the catalytic activity of the transition metal phosphates, in this paper, the cauliflower-like Co-W-P-O4/NF catalyst based on three-dimensional nickel foam was prepared by the method of element doping. The catalyst exhibited good bifunctional catalytic activity in alkaline solution. The prepared Co-W-P-O4/NF has a unique crystalline-amorphous phase structure with abundant active sites at the interface. In addition, W atoms can interact with Co atoms to co-optimise the electronic structure, enabling the Gibbs free energy of hydrogen adsorption (ΔGH*) to be close to 0, which is conducive to improving the performance of water electrolysis. To achieve a current density of 10 mA·cm−2, the Co-W-P-O4/NF required overpotentials of 42.1 mV for HER and 348.2 mV for OER in 1 M KOH solution, with the Tafel slopes being 48.0 and 83.6 mV·dec−1, respectively. When Co-W-P-O4/NF was used as both cathode and anode for water splitting, the two-electrode electrolyzer could achieve 10 mA·cm−2 with only 1.62 V, along with good stability.

First-principles study of the electronic and catalytic properties of nickel-antimony (Ni-Sb) alloy catalyst for hydrogen evolution reaction

Hydrogen evolution reaction (HER) is a vital half-reaction for water splitting to produce H2. Exploring efficient, affordably priced, and environmentally sustainable HER catalysts is necessary for the development of renewable energy conversion and storage technologies. Here, the HER catalytic activity of hexagonal NiSb(010), hexagonal NiSb(001), hexagonal NiSb(101), cubic Ni3Sb(100), cubic Ni3Sb(010), cubic Ni3Sb(101), orthorhombic Ni3Sb(010), and orthorhombic Ni3Sb(101), is systematically investigated by density functional theory methods. Based on the calculated surface energy, all the studied surfaces are stable. Subsequently, we further evaluate their HER activity by calculating Gibbs free energy of hydrogen adsorption (ΔG*H) and exchange current density (i0). The results show that hexagonal NiSb and orthorhombic Ni3Sb are expected to be promising HER catalysts in Ni-Sb alloys because their ΔG*H values are respectively −0.03 and 0.03 eV, and they have larger i0 values. The synergistic interaction between the metal atoms of Ni and Sb can effectively promote electron transfer between the catalyst and reaction species, which is clearly demonstrated by the electronic structure analysis, which also illustrates that such high catalytic activity can be attributed to it. This work is conducive to guiding the design of this kind of alloy electrocatalysts for HER.

Defect engineering of 1T′ MX 2 (M = Mo, W and X = S, Se) transition metal dichalcogenide-based electrocatalyst for alkaline hydrogen evolution reaction

The alkaline electrolyzer (AEL) is a promising device for green hydrogen production. However, their energy conversion efficiency is currently limited by the low performance of the electrocatalysts for the hydrogen evolution reaction (HER). As such, the electrocatalyst design for the high-performance HER becomes essential for the advancement of AELs. In this work, we used both hydrogen (H) and hydroxyl (OH) adsorption Gibbs free energy changes as the descriptors to investigate the catalytic HER performance of 1T′ transition metal dichalcogenides (TMDs) in an alkaline solution. Our results reveal that the pristine sulfides showed better alkaline HER performance than their selenide counterparts. However, the activities of all pristine 1T′ TMDs are too low to dissociate water. To improve the performance of these materials, defect engineering techniques were used to design TMD-based electrocatalysts for effective HER activity. Our density functional theory results demonstrate that introducing single S/Se vacancy defects can improve the reactivities of TMD materials. Yet, the desorption of OH becomes the rate-determining step. Doping defective MoS2 with late 3d transition metal (TM) atoms, especially Cu, Ni, and Co, can regulate the reactivity of active sites for optimal OH desorption. As a result, the TM-doped defective 1T′ MoS2 can significantly enhance the alkaline HER performance. These findings highlight the potential of defect engineering technologies for the design of TMD-based alkaline HER electrocatalysts.

Fe−N bonds induced highly efficient Fe3O4/g-C3N4 heterojunction for electrocatalytic hydrogen evolution

Fe-based catalysts with the merits of the most abundant reserves in the crust, cheapest, and low toxicity, show significant superiorities to noble-metal catalysts for electrocatalytic water splitting. Fe3O4 as a member of Fe-based catalysts has been widely used for oxygen evolution reaction (OER). However, it is rarely applied for Hydrogen evolution reaction (HER) owing to the lack of inherent active sites for hydrogen absorption. Fe−N coordination bonds can act as active sites for electrocatalytic performance. Therefore, we reasonably designed and constructed Fe3O4/g-C3N4 heterojunction, where abundant Fe−N bonds acting as HER active sites were formed with the aid of rich Pyridine N of g-C3N4. Activity characterization result indicates the optimized 50%-Fe3O4/g-C3N4 heterojunction exhibits excellent HER performance with a low overpotential of 160 mV at 10 mA cm−2, a low Tafel slope of 77.18 mV dec−1, and outstanding cycle stability. Density functional theory (DFT) calculation demonstrates that the enhanced electrocatalytic performance stems from the Fe−N bonding interaction, which endows 50%-Fe3O4/g-C3N4 with lower water dissociation barrier and a moderate Gibbs free energy of hydrogen adsorption (ΔGH*) in comparison with pristine Fe3O4 and g-C3N4.

Study of the molecular interaction of a phosphonium-based ionic liquid within myo-inositol and non-steroidal anti-inflammatory drugs.

Ionic liquids (ILs) can be used as carriers and solubilizers as well as for increasing the effectiveness of drugs. In the present investigation, the micellar properties of phosphonium-based ionic liquids (PILs) such as trihexyltetradecylphosphonium bis(2,4,4-trimethylpentyl)phosphinate ([P666(14)][THPP]) and the effect of carbocyclic sugar-based myo-inositol (MI) and non-steroidal anti-inflammatory drugs (NSAIDs), i.e. ibuprofen (IBU) or aspirin (ASP), on the PIL micellar system were studied using surface tension, conductivity, colorimetry, viscometry, FTIR, and dynamic light scattering (DLS) at a temperature of 299 ± 0.5 K. The critical micelle concentrations (CMCs), particle size, zeta potential, and various interfacial parameters were also included i.e., efficiency of adsorption (pC20), surface tension at CMC (γCMC), minimum surface area per molecule (Amin), surface pressure at CMC (πCMC), maximum surface excess concentration (Γmax), and various thermodynamic parameters, such as standard Gibbs free energy of adsorption , standard Gibbs free energy of micellization per alkyl tail , standard Gibbs free energy of the air-water interface (ΔG(s)min), standard Gibbs free energy of transfer , and standard Gibbs free energy of micellization . The adsorption and micellization characteristics became more spontaneous, as shown by the more negative values of and . Viscosity-based rheological properties were calculated for various PIL + MI and PIL + MI + NSAID systems. According to the DLS data, the PIL (Z = 316.4 nm) micellar system generates substantially bigger micelles in an aqueous solution of MI + ASP (Z = 801.7 nm) than in MI + IBU (Z = 674.7 nm). FTIR spectroscopy revealed the interactions of PIL with MI + ASP and MI + IBU, where it was observed that MI + IBU shows good agreement with the PIL system compared to MI + ASP. The current research will have effects on pharmaceutical sciences, molecular biology, and drug delivery.

Design and fabrication of intermetallic NiCo electrocatalysts for the alkaline HER.

The design and fabrication of highly efficient electrocatalysts are crucial for reducing energy consumption, improving hydrogen production rates, and prolonging the service life of alkaline electrolyzers. In this study, intermetallic L10-NiCo electrocatalysts were designed using DFT calculations and fabricated through a one-step solid-state reaction method. The DFT calculations indicated that L10-NiCo presented a lower H adsorption Gibbs free energy and a moderate H2O dissociation barrier compared to the commonly used Ni catalyst and disordered NiCo alloy. Increasing the solid-state reaction temperature facilitated the formation of intermetallic L10-NiCo. Electrocatalytic tests for the alkaline HER demonstrated that the ECSA of L10-NiCo nanoparticles increased to 2.3 times, the overpotential decreased by 19%, the electrocatalytic activity increased to 1.5 times, and the stability improved to 2.2 times compared to those of the Ni nanoparticles. This research provides insights into the design and fabrication of highly efficient catalytic electrodes for alkaline electrolyzers.

The regulatory function of the d-orbital structure in TM@g-t-C4N3 for bifunctional catalysis of the oxygen evolution/reduction reaction.

Highly efficient catalysts for the oxygen evolution/reduction reaction (OER/ORR) have attracted great attention in research for energy devices with high conversion efficiency. Herein, systematic first-principles investigations are performed to explore the catalytic performance of graphitic C4N3 loaded with single transition metal atoms (TM@g-t-C4N3) for the OER/ORR. The results show that Fe, Co, Ni and Rh@g-t-C4N3 exhibit fascinating bifunctional catalytic activities for both the OER and ORR. Moreover, it is observed that better activities are easily achieved when the valence d orbitals of doped TM atoms are nearly fully occupied. Further analysis reveals the volcano relationship between the OER/ORR performance and the adsorption Gibbs free energy. The adsorption free energy of intermediates in the OER/ORR process is also found to highly correlate with the electronic structures of TM@g-t-C4N3, which are mainly characterized by two quantities, one is the descriptor φ related to the electronegativity and the number of valence electrons in d orbitals, and the other is the projected d band center. The results indicate that it is possible to predict the catalytic performance of TM@g-t-C4N3 by a detailed examination of the electronic properties of the doped TM atoms to some extent. This research not only provides several highly active g-t-C4N3-based single-atom catalysts (SACs) for the OER/ORR, but also reveals some potential regularities of SAC systems.

Constructing interfacial electric field and Zn vacancy modulated ohmic junctions ZnS/NiS for photocatalytic H2 evolution

Adjusting the interfacial transport efficiency of photogenerated electrons and the free energy of hydrogen adsorption through interface engineering is an effective means of improving the photocatalytic activity of semiconductor photocatalysts. Herein, hollow ZnS/NiS nanocages with ohmic contacts containing Zn vacancy (VZn-ZnS/NiS) are synthesized using ZIF-8 as templates. An internal electric field is constructed by Fermi level flattening to form ohmic contacts, which increase donor density and accelerate electron transport at the VZn-ZnS/NiS interface. The experimental and DFT results show that the tight interface and VZn can rearrange electrons, resulting in a higher charge density at the interface, and optimizing the Gibbs free energy of hydrogen adsorption. The optimal hydrogen production activity of VZn-ZnS/NiS is 10636 μmol h-1 g-1, which is 31.9 times that of VZn-ZnS. This study provides an idea for constructing sulfide heterojunctions with ohmic contacts and defects to achieve efficient photocatalytic hydrogen production.

Organic-inorganic hybridization strategy for promoting BiOBr CO2 photoreduction via enhanced CO2 adsorption and photogenerated carrier migration

The low electron-hole separation efficiency and poor CO2 adsorption of BiOBr limit its photoreduction CO2 performance. In this work, BiOBr was hybridized with Ni-MOF, it shows that the Eads of BiOBr decreases from −0.36 eV to −1.73 eV, and the Gibbs free energy of CO2 adsorption decreases from 0.12 eV to −1.25 eV. In addition, the PL and TPR results reveal that the hybridization strategy accelerates the electron-hole separation rates. The CO evolution of BiOBr/Ni-MOF is 121.8 μmol g−1 h−1 when the amount of Ni-MOF is 15%, which is 5 and 7.2 times higher than BiOBr and Ni-MOF, respectively. Briefly, the CO2 adsorption and photogenerated carrier separation of inorganic materials can be improved by organic–inorganic hybridization strategy, which inspires a new direction for the design of high-performance catalysts.

Enhanced full-seawater splitting with a CoNiP@N,P-C core-shell electrocatalyst.

This study investigated a novel electrocatalyst with a core-shell structure of CoNiP@N,P-C. The unique carbon shell of this catalyst serves a dual purpose: exposing numerous active sites and safeguarding CoNiP nanoparticles from dissolution caused by the electrolyte. As a result, the CoNiP@N,P-C nanoparticles exhibit exceptional electrochemical properties. The CoNiP@N,P-C catalyst displays overpotentials of 234 and 314 mV for the HER and OER, respectively, within a simulated seawater solution (1 M KOH + 0.5 M NaCl), indicating its outstanding catalytic performance. Moreover, when subjected to full seawater splitting, the CoNiP@N,P-C catalyst exhibited high activity, achieving a 1.71 V cell voltage at a current density of 10 mA cm-2. As revealed by density functional theory (DFT) calculations, the CoNiP@N,P-C catalyst exhibits Gibbs free energy for hydrogen adsorption (ΔGH* = -0.19 eV) that is decreased in comparison with CoP@N,P-C, NiP@N,P-C, and N,P-C (-0.321 eV, -0.434 eV, and 0.723 eV, respectively). This finding confirms that the core-shell structure plays a role in enhancing the HER kinetics and improving the catalytic performance, which is consistent with the experimental observations. Consequently, this study introduces the concept of utilizing bimetal phosphide core-shell structures for overall seawater splitting, offering a novel approach in this field of research.

Design of a Single-Atom In-N3-S site to Modulate Exciton Behavior in Carbon Nitride for Enhanced Photocatalytic Performance.

Rational tailoring of the local coordination environment of single atoms has demonstrated a significant impact on the electronic state and catalytic performance, but the development of catalysts beyond noble/transition metals is profoundly significant and highly desired. Herein, the main-group metal indium (In) single atom is immobilized on sulfur-doped porous carbon nitride nanosheets (In@CNS) in the form of three nitrogen atoms coordinated with one sulfur atom (In-N3-S). Both theoretical calculations and advanced characterization investigations clearly elucidated that the single-atomic In-N3-S structures on In@CNS are powerful in promoting the dissociation of excitons into more free carriers as well as the charge separation, synergistically elevating electron concentration by 2.19 times with respect to pristine CNS. Meanwhile, the loading of In single atoms on CNS is responsible for altering electronic structure and lowering the Gibbs free energy for hydrogen adsorption. Consequently, the optimized In@CNS-5.0 exhibited remarkable photocatalytic performance, remarkable water-splitting and tetracycline hydrochloride degradation. The H2 production achieved to 10.11mmolh-1g-1 with a notable apparent quantum yield of 19.70% at 400nm and remained at 10.40% at 420nm. These findings open a new perspective for in-depth comprehending the effect of the main-group metal single-atom coordination environment on promoting photocatalytic performance.

Universal Platform for Robust Dual-Atom Doped 2D Catalysts with Superior Hydrogen Evolution in Wide pH Media.

Layered 2D transition metal dichalcogenides (TMDs) have been suggested as efficient substitutes for Pt-group metal electrocatalysts in the hydrogen evolution reaction (HER). However, poor catalytic activities in neutral and alkaline electrolytes considerably hinder their practical applications. Furthermore, the weak adhesion between TMDs and electrodes often impedes long-term durability and thus requires a binder. Here, a universal platform is reported for robust dual-atom doped 2D electrocatalysts with superior HER performance over a wide pH range media. V:Co-ReS2 on a wafer scale is directly grown on oxidized Ti foil by a liquid-phase precursor-assisted approach and subsequently used as highly efficient electrocatalysts. The catalytic performance surpasses that of Pt group metals in a high current regime (≥ 100mA cm-2) at pH ≥ 7, with a high durability of more than 70h in all media at 200mA cm-2. First-principles calculations reveal that V:Co dual doping in ReS2 significantly reduces the water dissociation barrier and simultaneously enables the material to achieve the thermoneutral Gibbs free energy for hydrogen adsorption.

Nanocages and nanotubes as catalysts for ORR and OER processes

The capacities, abilities and potential of Ni–C36, Ni–Al18P18, Co–C54, Co–Ge54, Co-CNT(7, 0), Co-GeNT(7, 0), Ni-CNT(10, 0) and Ni-AlPNT(10, 0) to use as catalysts of OER and ORR are examined by theoretical models. The adsorption energy, free Gibbs adsorption energy, overpotential and Gibbs free energy values of ORR and OER on used catalysts are compared with other metal catalysts. The Ni and Co atoms which are doped on nanotubes and nanocages are catalytic positions to adsorb ORR and OER species the and to process the reaction steps of OER and ORR. The Co-GeNT(7, 0) and Ni-AlPNT(10, 0) have lower overpotential than Ni–C36, Ni–Al18P18, Co–C54 and Co–Ge54. Finally, the Co-GeNT(7, 0) and Ni-AlPNT(10, 0) are suggested as catalysts with acceptable stability, high capacity to adsorb the species, lower over-potential and high performances by theoretical models.

Electrode Imbibition and Surfactant Interactions with Vanadium Flow Battery Electrolytes

Redox flow batteries (RFB) are a critical technology for stationary grid-scale energy storage, with potential usage with intermittent power sources, such as wind and solar. RFBs are attractive for long-duration energy storage because the anolyte and catholyte are stored separately external to the electrochemical reactor. Separating the electrolytes and the electrochemical cell decouples energy and power densities, unlike batteries that store charge in the solid-state, such as Li-ion, Pb-acid, or Ni-Cd. A standard RFB chemistry is the all-vanadium redox flow battery (VRFB), which utilizes the four oxidation states of vanadium, with V2+, V3+, V4+, and V5+. Recently our group found that adding small amounts of sodium dodecyl sulfate (SDS) to a VFRB increased the kinetics of the V2+ to V3+oxidation.Furthermore, surfactants play essential roles in battery manufacturing and operation. Surfactants can change metal oxide crystal structure, inhibit dendrite growth, limit corrosion, and prevent nanoparticle agglomeration. Surfactants are never wholly removed during manufacturing and can be present during battery operation. Therefore, it is crucial to understand how surfactants impact battery performance and their effect on the materials.This talk describes SDS's equilibrium surface properties and adsorption characteristics at the liquid−air and liquid-solid interfaces, thus providing insights into the interactions of SDS with a VFRB electrolyte. Experiments focusing on the effects of sulfuric acid and vanadium ions on SDS's equilibrium surface tension and critical micelle concentration (CMC) were completed. The Szyszkowski equation is used to calculate SDS's adsorption parameters, such as interfacial surface excess, Γsz [mol/m2], the surface excess at the saturated interface, Γ∞ [mol/m2], the minimum molecular area in the adsorption layer at the saturated interface, Amin [nm2], and the Gibbs free energy of adsorption, ΔGads [kJ/mol]. Furthermore, an examination of the spontaneous imbibition of the VFRB electrolyte with SDS into a porous carbon electrode is presented. The microstructure of porous systems, interfacial tension, and fluid−solid interactions controls the capillary-driven flow and is vital in multiphase flow in porous media. Therefore, understanding SDS's effects on the VFRB electrolyte in an electrode is critical to understanding the electrochemical reactions and molecular interactions occurring.This work was supported as part of the Breakthrough Electrolytes for Energy Storage and Systems (BEES2), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award # DE-SC0019409.

High Surface Area MoS2 and WS2 As Active HER Catalysts

The ever-increasing demand for clean energy necessitates a widespread adoption of clean energy carriers, namely green hydrogen. However, its production via electrolysis remains expensive. To achieve the needed drop in production cost, efficient catalyst materials are sought after to overcome the energy barrier of water splitting. Transition metal dichalcogenides (TMDCs) such as tungsten and molybdenum disulfide (WS2, MoS2) have been identified as promising catalysts because of their remarkably low Gibbs free energy for hydrogen adsorption.[1] The main challenge for these materials is the precise fabrication of continuous (mono)layers to achieve the desired functional properties.[2] Bottom-up material fabrication approaches like the vapor phase methods CVD and ALD offer several advantages. The use of chemical reactions of gas phase species allows precise thickness control, high quality films and allow large areas to be coated.This study focused on the fabrication of WS2 and MoS2 layers via metal organic chemical vapor deposition (MOCVD) and subsequent investigation of the properties of the resulting films in relation to the applied process conditions. Depositions were performed on FTO substrates and their thickness dependent capability to catalyze the electrochemical hydrogen evolution reaction (HER) were investigated in detail.For WS2 the selective growth of the semiconducting hexagonal phase with the targeted stoichiometry at a deposition temperature of 600°C was achieved (Fig 1 a). Similarly, in the case of MoS2, the hexagonal phase could be selectively deposited from 400 °C onwards and with pronounced crystallinity at 600°C (Fig. 1 b) which also showed the best stochiometric match and highest purity. The thin film characterization was further supported by Raman spectroscopy which serves as probe to verify the formed phase and layer number for 2D-materials. UV-VIS spectroscopy was employed to assess the semiconducting behavior allowing for band gap determination via the Tauc plot. Morphology and surface topography, especially interesting in the realm of HER catalysis, were assessed by SEM and HR-TEM showing the typical flakelike features known for these materials in their hexagonal phase (Fig 1 c). Electrochemical LSV experiments of WS2 in H2SO4 showed thickness dependence of the overpotentials which correlates with the flake density and the availability of vertical edge sites most active for HER (Fig 1 d). Similar studies for MoS2 are ongoing. These results are especially noteworthy as previous studies on WS2 deposited onto FTO have reported notably higher overpotentials.[3,4] This study demonstrates the potential of large area and high surface area TMDCs as effective HER electrocatalysts.[1] S. H. Noh, J. Hwang, J. Kang, M. H. Seo, D. Choi, B. Han, J. Mater. Chem. A 2018, 6, 20005–20014.[2] K. S. Novoselov, D. Jiang, A. K. Geim, et al. Proc. Natl. Acad. Sci. U.S.A. 2005, 102, 10451–10453.[3] J.-L. Wree, J.-P. Glauber, A. Devi, et al. J. Mater. Chem. C 2021, 9, 10254–10265.[4] J.-L. Wree, E. Ciftyurek, A. Devi, et al. Dalton Trans. 2020, 49, 13462–13474. Figure 1

Nickel-Based Bifunctional Cocatalyst to Enhance CdS Photocatalytic Hydrogen Production.

The design of nanocomposites as a light-capturing system applied in photocatalytic water splitting is an emerging area of research. In our study, a simple in situ photodeposition method was proposed for the synthesis of CdS nanoflowers modified by nickel-based bifunctional, i.e., Ni/Ni(OH)2, cocatalysts. The introduction of cocatalysts has demonstrated a notable enhancement in the photocatalytic hydrogen evolution efficiency of CdS. The quantity of cocatalysts supported on CdS played an important role in governing the light absorption capability and photocatalytic efficacy. Ni-CdS-10 showed the best photocatalytic activity of 30.51 mmol g-1 h-1, which was 1.8 times and 2.6 times higher activity than Pt-CdS-1 wt % and pure CdS, respectively. Mechanism studies with UV-vis DRS, photoluminescence, and Mott-Schottky plots revealed the intrinsic electric field created at the p-n Ni(OH)2/CdS junctions, which can effectively implement the transport and separation of photoinduced carriers. From linear sweep voltammetry, electrochemical impedance spectroscopy, and DFT calculation, both Ni(OH)2 and Ni can effectively decrease the Gibbs free energies of hydrogen adsorption and reduce the overpotential of hydrogen evolution. As a result, the efficiency of generating H2 through photocatalysis experienced significant improvement, and the participation of bifunctional cocatalysts further reduced the photocorrosion of CdS, enhanced stability, improved low price, and efficient photocatalyst production.

DFT Investigation of CH4 and H2O Adsorption on Pd (111), Ni (111), Pt (111), and Ir(111) Surfaces

Using density functional theory (DFT) calculations, the surface Gibbs free energy of methane and water adsorption on Pt(111), Ir(111), Ni(111), and Pd(111) surfaces was investigated. DFT computations were employed to investigate the adsorption of methane and water molecules on unit cells with varying coverage levels of 0.11, 0.25, 0.50, and 1.00 monolayers and the aggregation of H2O over clean transition metal surfaces. The adsorption configuration was assessed to experimental findings to evaluate our computational approaches' accuracy and reliability. A thermodynamic diagram was constructed for exploring the adsorption of CH4 and H2O on metal surfaces. The order of the methane adsorption energies on different metal surfaces is as follows: Pd(111) > Pt(111) > Ni(111) > Ir(111). A more significant number of H2O molecules on the transition metal surfaces reduces the contact between the metal surfaces and water molecules during water aggregation. The thermodynamic stability of water and methane adsorption coverage was found to be best on the Pt(111) surface.

Enabling Internal Electric Field in Heterogeneous Nanosheets to Significantly Accelerate Alkaline Hydrogen Electrocatalysis.

Efficient bifunctional hydrogen electrocatalysis, encompassing both hydrogen evolution reaction (HER) and hydrogen oxidation reaction (HOR), is of paramount significance in advancing hydrogen-based societies. While non-precious-metal-based catalysts, particularly those based on nickel (Ni), are essential for alkaline HER/HOR, their intrinsic catalytic activity often falls short of expectations. Herein, an internal electric field (IEF) strategy is introduced for the engineering of heterogeneous nickel-vanadium oxide nanosheet arrays grown on porous nickel foam (Ni-V2O3/PNF) as bifunctional electrocatalysts for hydrogen electrocatalysis. Strikingly, the Ni-V2O3/PNF delivers 10mAcm-2 at an overpotential of 54mV for HER and a mass-specific kinetic current of 19.3Ag-1 at an overpotential of 50mV for HOR, placing it on par with the benchmark 20% Pt/C, while exhibiting enhanced stability in alkaline electrolytes. Density functional theory calculations, in conjunction with experimental characterizations, unveil that the interface IEF effect fosters asymmetrical charge distributions, which results in more thermoneutral hydrogen adsorption Gibbs free energy on the electron-deficient Ni side, thus elevating the overall efficiency of both HER and HOR. The discoveries reported herein guidance are provided for further understanding and designing efficient non-precious-metal-based electrocatalysts through the IEF strategy.