Black Phosphorus-Graphene Heterostructure-Supported Pd Nanoparticles with Superior Activity and Stability for Ethanol Electro-oxidation

Modification Strategies for Development of 2D Material-Based Electrocatalysts for Alcohol Oxidation Reaction

2D materials, such as graphene, MXenes (metal carbides and nitrides), graphdiyne (GDY), layered double hydroxides, and black phosphorus, are widely used as electrocatalyst supports for alcohol oxidation reactions (AORs) owing to their large surface area and unique 2D charge transport channels. Furthermore, the development of highly efficient electrocatalysts for AORs via tuning the structure of 2D support materials has recently become a hot area. This article provides a critical review on modification strategies to develop 2D material-based electrocatalysts for AOR. First, the principles and influencing factors of electrocatalytic oxidation of alcohols (such as methanol and ethanol) are introduced. Second, surface molecular functionalization, heteroatom doping, and composite hybridization are deeply discussed as the modification strategies to improve 2D material catalyst supports for AORs. Finally, the challenges and perspectives of 2D material-based electrocatalysts for AORs are outlined. This review will promote further efforts in the development of electrocatalysts for AORs.

D-Band Engineering in Pd-Based Nanowire Networks for Further Enhancement in Ethanol Electrooxidation Reaction

The development of highly efficient electrocatalysts for the ethanol oxidation reaction (EOR) is essential for the commercialization of direct ethanol fuel cells, yet challenges remain. In this study, a one-pot solution-phase method to synthesize Pd nanowire networks (NNWs) with very high surface-to-volume ratio having numerous twin and grain boundaries is developed. Using the same method, the Pd lattice is further engineered by introducing Ag and Cu atoms to produce AgPd, and CuPd alloy structure which significantly shifts the Pd d-band center upward and downward, respectively due to strain and ligand effects. Theoretical analysis employing density functional theory (DFT) demonstrates that such modification of the d-band center significantly influences the adsorption energies of reactants on the catalytic surface. Owing to their notably high surface-to-volume ratio and the presence of multiple twin and grain boundaries, Pd NNWs demonstrate significantly enhanced electrocatalytic activity toward EOR, ≈7.2 times greater than that of commercial Pd/C. Remarkably, compared to Pd NNWs, AgPd, and CuPd NNWs display enlarged and reduced electrocatalytic activity toward EOR, respectively. Specifically, Ag4Pd7 NNWs achieve a remarkable mass activity of 9.00 A mgpd -1 for EOR, which is 13.6 times higher than commercial Pd/C.

Rational Design and Facile Preparation of Palladium-Based Electrocatalysts for Small Molecules Oxidation

Direct liquid fuel cells (DLFCs) can convert the chemical energy of small organic molecules directly into electrical energy, which is a promising technique and always calls for electrocatalysts with high activity, stability and selectivity. Palladium (Pd)-based catalysts for DLFCs have been widely studied with the pursuit of ultra-high performance, however, most of the preparation routes require complex agents, multi-operation steps, even extreme experimental conditions, which are high-cost, energy-consuming, and not conducive to the scalable and sustainable production of catalysts. In this review, the recent progresses on not only the rational design strategies, but also the facile preparation methods of Pd-based electrocatalysts for small molecules oxidation reaction (SMOR) are comprehensively summarized. Based on the principles of green chemistry in material synthesis, the basic rules of "facile method" have been restricted, and the fabrication processes, perks and drawbacks, as well as practical applications of the "real" facile methods have been highlighted. The landscape of this review is to facilitate the mild preparation of efficient Pd-based electrocatalysts for SMOR, that is, to achieve a balance between "facile preparation" and "outstanding performance", thereby to stimulate the huge potential of sustainable nano-electrocatalysts in various research and industrial fields.

Nano-based biofuel production from low-cost lignocellulose biomass: environmental sustainability and economic approach

The use of nanomaterials in biofuel production from lignocellulosic biomass offers a promising approach to simultaneously address environmental sustainability and economic viability. This review provides an overview of the environmental and economic implications of integrating nanotechnology into biofuel production from low-cost lignocellulosic biomass. In this review, we highlight the potential benefits and challenges of nano-based biofuel production. Nanomaterials provide opportunities to improve feedstock pretreatment, enzymatic hydrolysis, fermentation, and catalysis, resulting in enhanced process efficiency, lower energy consumption, and reduced environmental impact. Conducting life cycle assessments is crucial for evaluating the overall environmental footprint of biofuel production. An economic perspective that focuses on the cost implications of utilizing nanomaterials in biofuel production is also discussed. A comprehensive understanding of both environmental and economic dimensions is essential to fully harness the potential of nanomaterials in biofuel production from lignocellulosic biomass and to move towards sustainable future energy.

Ultrafast synthesis of efficient TS-PtCoCu/CNTs composite with high feed-to-product conversion rate by Joule heating for electrocatalytic oxidation of ethanol

Due to the challenges involved in achieving high metal load, uniform metal dispersion and nanosized metal particles simultaneously, it is difficult to develop a simple protocol for the rapid and efficient synthesis of Pt-based composites for electrocatalytic ethanol oxidation reaction (EOR). In this study, a facile ultrafast thermal shock strategy via Joule heating was applied to fabricate a series of PtCoCu ternary nanoalloys decorated carbon nanotube composites (TS-PtCoCu/CNTs), without the need for a reducing agent or surfactant. The TS-PtCoCu/CNTs with optimal Pt content (∼15 %) exhibited excellent EOR activity, with mass and specific activity of 3.58 A mgPt-1 and 5.79 mA cm-2, respectively, which are 3.8 and 13.5 times higher than those of Pt/C. Compared with the control prepared through the traditional furnace annealing, the catalyst also showed excellent activity and stability. DFT calculations revealed that the TS-PtCoCu/CNTs possesses a downshifted d-band center, weakened CO adsorption and higher OH affinity compared with monometallic Pt, all of which lead to the preferred C1 pathway for EOR. This study demonstrates an ultrafast construction of a highly efficient Pt-Co-Cu ternary catalyst for EOR. Additionally, it provides insights into the reaction mechanism based on structural characterization, electrochemical characterization, and theoretical calculations.

Efficient oxidation of benzyl alcohol into benzaldehyde catalyzed by graphene oxide and reduced graphene oxide supported bimetallic Au-Sn catalysts

A series of bimetallic and monometallic catalysts comprising Au and Sn nanoparticles loaded on graphene oxide (GO) and reduced graphene oxide (rGO) were prepared using three distinct techniques: two-step immobilization, co-immobilization, and immobilization. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), energy dispersive X-ray (EDX), and Inductively-coupled plasma optical emission spectroscopy (ICP-OES) were used to characterize the chemical and physical properties of prepared Au-Sn bimetallic and Au or Sn monometallic nanocatalysts. The catalytic performance of the prepared nanocatalysts was evaluated in the selective oxidation of benzyl alcohol (BzOH) to benzaldehyde (BzH) using O2 as an oxidizing agent under moderate conditions. To obtain the optimal BzH yield, the experimental conditions and parameters, including the effects of the reaction time, temperature, pressure, and solvent type on BzOH oxidation, were optimized. Under optimal reaction conditions, bimetallic Au-Sn nanoparticles supported on GO (AuSn/GO-TS, 49.3%) produced a greater yield of BzH than the AuSn/rGO-TS catalysts (35.5%). The Au-Sn bimetallic catalysts were more active than the monometallic catalysts. AuSn/GO-TS and AuSn/rGO-TS prepared by the two-step immobilization method were more active than AuSn/GO-CoIM and AuSn/rGO-CoIM prepared by co-immobilization. In addition, the AuSn/GO-TS and AuSn/rGO-TS catalysts were easily separated from the mixture by centrifugation and reused at least four times without reducing the yield of BzH. These properties make Au-Sn bimetallic nanoparticles supported on GO and rGO particularly attractive for the environmentally friendly synthesis of benzaldehyde.

Synthesis of Zn3V2O8/rGO Nanocomposite for Photocatalytic Hydrogen Production

In this study, zinc vanadate/reduced graphene oxide (Zn3V2O8/rGO) composite has been synthesized via a simple approach. Advanced characterization techniques (powder X-ray, scanning electron microscopy, energy dispersive X-ray spectroscopy and ultraviolet-visible (UV-vis) spectroscopy) have been used to authenticate the formation of Zn3V2O8/rGO composite. Subsequently, Zn3V2O8/rGO was applied as photo-catalyst for hydrogen generation using photo-catalysis. The Zn3V2O8/rGO photo-catalyst exhibited a good hydrogen generation amount of 104.6 µmolg−1. The Zn3V2O8/rGO composite also demonstrates excellent cyclic stability which indicated better reusability of the photo-catalyst (Zn3V2O8/rGO). This work proposes a new photo-catalyst for H2 production application. We believe that the presence of synergistic interactions was responsible for the improved photo-catalytic properties of Zn3V2O8/rGO composite. The Zn3V2O8/rGO composite is an environmentally friendly and cost-effective photo-catalyst and can be used for photo-catalytic applications.

Black phosphorous/palladium functionalized carbon aerogel nanocomposite for highly efficient ethanol electrooxidation

Direct ethanol fuel cells have great potential for practical power applications due to their easy operation, high energy density, and low toxicity. However, the slow and incomplete ethanol electrooxidation (EEO) reaction is a major drawback that hinders the development of this type of fuel cell. Here, we report a facile approach for the preparation of highly active, low cost and stable electrocatalysts based on palladium (Pd) nanoparticles and black phosphorus/palladium (BP/Pd) nanohybrids supported on a carbon aerogel (CA). The nanocomposites show remarkable catalytic performance and stability as anode electrocatalysts for EEO in an alkaline medium. A mass peak current density of 8376 mA mg_Pd ^-1 is attained for EEO on the BP/Pd/CA catalyst, which is 11.4 times higher than that of the commercial Pd/C catalyst. To gain deep insight into the structure-property relationship associated with superior electroactivity, the catalysts are well characterized in terms of morphology, surface chemistry, and catalytic activity. It is found that the BP-doped CA support provides high catalyst dispersibility, protection against leaching, and modification of the electronic and catalytic properties of Pd, while the catalyst modifies CA into a more open and conductive structure. This synergistic interaction between the support and the catalyst improves the transport of active species and electrons at the electrode/electrolyte interface, leading to rapid EEO reaction kinetics.

Synthesis of Pd nanorod arrays on Au nanoframes for excellent ethanol electrooxidation

Au-Pd hollow nanostructures have attracted a lot of attention because of their excellent ethanol electrooxidation performance. Herein, we report a facile preparation of Au nanoframe@Pd array electrocatalysts in the presence of cetylpyridinium chloride. The reduced Pd atoms were directed to mainly deposit on the surface of the Au nanoframes in the form of rods, leading to the formation of Au nanoframe@Pd arrays with a super-large specific surface area. The red shift and damping of the plasmon peak were ascribed to the deposition of the Pd arrays on the surface of the Au nanoframes and nanobipyramids, which was verified by electrodynamic simulations. Surfactants, temperature and reaction time determine the growth process and thereby the architecture of the obtained Au-Pd hollow nanostructures. Compared with the Au nanoframe@Pd nanostructures and Au nanobipyramid@Pd arrays, the Au nanoframe@Pd arrays exhibit an enhanced electrocatalytic performance towards ethanol electrooxidation due to an abundance of catalytic active sites. The Au NF@Pd arrays display 4.1 times higher specific activity and 13.7 times higher mass activity than the commercial Pd/C electrocatalyst. Moreover, the nanostructure shows improved stability towards the ethanol oxidation reaction. This study enriches the manufacturing technology to increase the active sites of noble metal nanocatalysts and promotes the development of direct ethanol fuel cells.

A Critical Review on Black Phosphorus-Based Photocatalytic CO2 Reduction Application

Energy shortages and greenhouse effects are two unavoidable problems that need to be solved. Photocatalytically converting CO₂ into a series of valuable chemicals is considered to be an effective means of solving the above dilemmas. Among these photocatalysts, the utilization of black phosphorus for CO₂ photocatalytic reduction deserves a lightspot not only for its excellent catalytic activity through different reaction routes, but also on account of the great preponderance of this relatively cheap catalyst. Herein, this review offers a summary of the recent advances in synthesis, structure, properties, and application for CO₂ photocatalytic reduction. In detail, the review starts from the basic principle of CO₂ photocatalytic reduction. In the following section, the synthesis, structure, and properties, as well as CO₂ photocatalytic reduction process of black phosphorus-based photocatalyst are discussed. In addition, some possible influencing factors and reaction mechanism are also summarized. Finally, a summary and the possible future perspectives of black phosphorus-based photocatalyst for CO₂ reduction are established.

Rich grain boundaries endow networked PdSn nanowires with superior catalytic properties for alcohol oxidation

Networked nanowire (NNW)-structured catalysts have attracted extensive attention due to their large surface area and structural stability, which mean that they have excellent catalytic activity and stability and can be used as anode reaction catalysts for use in direct alcohol fuel cells (DAFCs). Herein, a series of networked PdSn nanowires synthesized via a modified polyol strategy are used as efficient DAFCs anode reaction catalysts. The introduction of Sn plays an important role in the improvement of catalytic behavior, in which the existence of Sn promotes the oxidation of intermediates by providing abundant oxyphilic species. Moreover, the generated PdSn NNWs-3 with optimal content show rich grain boundaries and an even NNW structure, which provides more active sites to further improve catalytic performance, so it exhibits excellent activity toward alcohol oxidation. The mass activities of PdSn NNWs-3 toward the ethanol oxidation reaction (EOR) and the methanol oxidation reaction (MOR) are 8105.0 and 3099.5 mA mg_Pd^-1, which are 6.9 and 10.7 times higher than those of Pd/C, respectively. Compared with Pd/C, the PdSn NNWs also display enhanced stability towards the EOR and MOR. This work demonstrates that NNW nanocatalysts indeed exhibit excellent catalytic performance for alcohol oxidation reactions.

Recent advances in phosphorus containing noble metal electrocatalysts for direct liquid fuel cells

Direct liquid fuel cells (DLFCs) are considered as satisfactory alternatives to traditional fossil fuels owing to their unique advantages, e.g. environmental friendliness and easy storage. Noble metal catalysts are widely used to improve the efficiency of DLFCs. However, the high cost, low utilization and poor stability of noble metals restricted their practical applications. Therefore, it is of great significance to explore cost-effective electrocatalysts and further improve their electrocatalytic performance. Reducing the content of noble metals by adding low-priced phosphorus (P) has been considered as an effective strategy, which is able to enhance their electrocatalytic activity and anti-poisoning ability through effectively changing the electronic density of active sites. In the past few years, tremendous P containing catalysts have been synthesized and utilized in DLFCs. In this review, we summarize the fundamentals of electrochemical reactions and present recent progress in P containing noble metal catalysts for DLFCs, including the discussion of their shape, composition and the relationship between P and active sites. Finally, the challenges and some potential directions in this field are pointed out.

Highly efficient blackberry-like trimetallic PdAuCu nanoparticles with optimized Pd content for ethanol electrooxidation

The rational design of highly efficient catalysts for ethanol electrooxidation is extremely challenging for developing direct ethanol fuel cells (DEFCs). Herein, a facile one-pot method has been developed to prepare blackberry-like PdAuCu nanoparticles (NPs) with tunable composition and surface structures. Among PdAuCu NPs with different Pd contents (1.6-22 mass%), PdAuCu NPs-0.5 (contained Pd at 2.5 mass%) delivered one of the highest catalytic activities of Pd-based catalysts towards ethanol electrooxidation, exhibiting a mass activity of 23.0 A mg_Pd^-1. Kinetic analysis, electrochemical impedance spectroscopy and CO stripping test results suggested that the excellent electrocatalytic activity may originate from the optimized balance between Pd content and surface structure of PdAuCu NPs-0.5. The optimization of the balance between composition and surface structure would contribute to the further design of multimetallic nanoparticles for fuel cells and other applications.

Trimetallic synergy in dendritic intermetallic PtSnBi nanoalloys for promoting electrocatalytic alcohol oxidation

Developing effective and robust novel electrocatalysts for direct alcohol fuel cells has been gaining much attention. However, the widely used Pt catalyst suffers from limitations including the sluggish kinetics, severe CO poisoning, and catalyst lost caused by aggregation and Ostwald ripening during alcohol oxidation reaction. Herein, dendritic intermetallic PtSnBi nanoalloys were synthesized via a facile hydrothermal approach with high electrocatalytic performance and enhanced CO resistance for methanol oxidation reaction (MOR) and ethanol oxidation reaction (EOR) owing to the synergism of the chosen three elements and unique three-dimensional morphology. Specifically, the PtSnBi nanoalloys display 4.6 and 6.7 times higher of mass activity (7.02 A mg^-1_Pt) and specific activity (16.65 mA cm^-2) toward MOR than those of commercial Pt/C, respectively. The mass activity of PtSnBi nanoalloys still retains 75.7% of the initial value after 800 cycles of stability test, superior to Pt/C (38.0%). The dual-functional effect of Sn, optimized electronic structure by the ligand effect, and unique atomic arrangement are responsible for the enhanced MOR activity and stability of PtSnBi nanoalloys. Furthermore, the PtSnBi nanoalloys with highlighted anti-CO poisoning capacity also improve the electrocatalytic performance toward EOR, indicating their great promise as broad energy electrocatalysts.

Potential-Dependent Mechanistic Study of Ethanol Electro-oxidation on Palladium

We herein used the density functional theory (DFT) method and the implicit continuum solvation model to study the potential-dependent mechanism of ethanol oxidation reaction (EOR) on palladium (Pd). Energy evolutions of the EOR on low-index Pd surfaces, including (111), (110), and (100), were obtained as a function of the electrode potential. Moreover, the onset potentials for key intermediates and products were calculated. In addition, the potential range for adsorbed ethanol as the most stable adsorption state for proceeding the EOR was determined to be between 0.15 and 0.78 V via the calculated Pourbaix diagrams when considering hydrogen underpotential deposition and Pd(II) oxide formation as competing reactions. Specifically, the behavior of Pd(111) as the dominating facet decided the overall activity of the EOR with onset potentials to acidic acid/acetate at 0.40 V, to carbon dioxide at 0.71 V, and to oxide formation at 0.78 V. Pd(110) was predicted to exhibit the optimal activity toward the EOR with the lowest onset potentials to both the first dehydrogenation process and carbon dioxide at 0.08 and 0.60 V, respectively. A computational potential-dependent mechanism of the EOR was proposed, which agrees well with the experimental curve of linear sweeping voltammetry on the commercial Pd/C electrocatalyst. Our study suggests that targeted control of products can be tuned with proper overpotential and thus provides a foundation for the future development of EOR electrocatalysts.

Enhancing electrocatalytic water splitting by surface defect engineering in two-dimensional electrocatalysts

Overall electrocatalytic water splitting can efficiently and sustainably produce clean hydrogen energy to alleviate the global energy crisis and environmental pollution. Two-dimensional (2D) materials with a unique band structure and surface conformation have emerged as promising electrocatalysts for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). However, the intrinsic activities of primitive 2D materials in the catalytic process are still inferior to those of noble metal-based electrocatalysts. Surface defect engineering can modulate the electronic structure of 2D materials and induce new physicochemical properties, promoting their electrocatalytic performance. Herein, this minireview focuses on some recent developments in surface defect engineering, including the contribution of active sites, the derivation of the heterogeneous interface, and the anchoring of active substances, which provides an effective way to further optimize 2D electrocatalysts for water splitting. Furthermore, the typical morphological characteristics, catalytic activity, stability and catalytic mechanism of these 2D electrocatalysts are introduced. We believe that this minireview will help design more efficient and economical electrocatalysts for overall water splitting.

The Art of Constructing Black Phosphorus Nanosheet Based Heterostructures: From 2D to 3D

Assembling different kinds of 2D nanosheets into heterostructures presents a promising way of designing novel artificial materials with new and improved functionalities by combining the unique properties of each component. In the past few years, black phosphorus nanosheets (BPNSs) have been recognized as a highly feasible 2D material with outstanding electronic properties, a tunable bandgap, and strong in-plane anisotropy, highlighting their suitability as a material for constructing heterostructures. In this study, recent progress in the construction of BPNS-based heterostructures ranging from 2D hybrid structures to 3D networks is discussed, emphasizing the different types of interactions (covalent or noncovalent) between individual layers. The preparation methods, optical and electronic properties, and various applications of these heterostructures-including electronic and optoelectronic devices, energy storage devices, photocatalysis and electrocatalysis, and biological applications-are discussed. Finally, critical challenges and prospective research aspects in BPNS-based heterostructures are also highlighted.

Gas-solid two-phase flow (GSF) mechanochemical synthesis of dual-metal-organic frameworks and research on electrochemical properties

As an alternative approach for conventional mechanochemical synthesis, a novel gas-solid two-phase flow (GSF) synthetic technique for the mechanochemical synthesis of dual metal-organic frameworks (DMOFs) was reported for the first time. The prepared CoMn₂(BTC)₂ was characterized by FT-IR, DTA, TG/DTG, and XRD studies. The results indicated that CoMn₂(BTC)₂ (BTC = 1,3,5-benzenetricarboxylate) was successfully synthesized after 10 min at a rate of 60 kg h^-1. CoMn₂O₄ microspheres were also prepared via the CoMn₂(BTC)₂ precursor method and characterized using FT-IR, XPS, XRD, SEM, EDS, and BET methods. The electrochemical properties of the as-prepared CoMn₂O₄ were investigated, and the GSF results showed that the microsphere electrodes of CoMn₂O₄ had a high specific capacitance (969 F g^-1) at a current density of 1 A g^-1 in 3 M aqueous KOH solution.

Single-Step Synthesis of Platinoid-Decorated Phosphorene: Perspectives for Catalysis, Gas Sensing, and Energy Storage

The originality of phosphorene is suppressed by its structural defects, irreproducibility, and sensitivity to the ambient environment. To preserve phosphorene's essential characteristics, for example, influencing the charge redistribution and generating the formation of active centers, noble-metal decoration is found to be an efficient approach. Herein, we demonstrate a single-step electrochemical synthesis of platinoid-decorated few-layer phosphorene (FP). The material's structure and effects of metal (Ru, Rh, and Pd) deposition on the FP nanosheets were first explored by numerous analytical techniques and theoretical calculations. Platinoid-decorated FPs demonstrate high quality and consist of one to five layers modified with round- and heptagon-shaped metal nanoparticles with the most intense distribution of Pd. The high-rate Rh deposition provides the enhanced electrocatalytic efficiency for hydrogen evolution (79 mV·dec^-1-Tafel slope) and almost 20 times increased capacity for the Li-ion batteries in comparison to bare and Ru-decorated FP. The chemosensing of platinoid-decorated FP indicates a response to methanol plus ethanol and shows inertness to acetone. The incorporation of Ru and Rh nanoparticles increases FP's selectivity toward methanol. This research provides a new approach for the in situ FP functionalization during top-down synthesis and thus broadens the material's feasibility for advanced nanotechnology.

Far-infrared and terahertz emitting diodes based on graphene/black-P and graphene/MoS2 heterostructures

We propose the far-infrared and terahertz emitting diodes (FIR-EDs and THz-EDs) based on the graphene-layer/black phosphorus (GL/b-P) and graphene-layer/MoS₂ (GL/MoS₂) heterostructures with the lateral hole and vertical electron injection and develop their device models. In these EDs, the GL serves as an active region emitting the FIR and THz photons. Depending on the material of the electron injector, the carriers in the GL can be either cooled or heated dictated by the interplay of the vertical electron injection and optical phonon recombination. The proposed EDs based on GL/b-P heterostructures can be efficient sources of the FIP and THz radiation operating at room temperature.

Enhancement of the performance of Pd nanoclusters confined within ultrathin silica layers for formic acid oxidation

The optimized design of highly active and stable anode electrocatalysts is essential for high performance direct formic acid fuel cells (DFAFCs). Herein, a facile and cost-effective strategy was proposed to fabricate a robust ultrasmall Pd nanocluster confined within ultrathin protective silica layers anchored on nitrogen doped reduced GO (NrGO) through generating amine functionalized graphene oxide with 3-aminopropyl triethoxysilane (APTES), followed by tuning the thickness of protective silica layers by precisely controlling the amount of tetraethylorthosilicate (TEOS). Amine functionalized graphene oxide generated by using APTES favors the formation of ultrasmall Pd nanoclusters due to the coordination of amine to PdCl24- while the confinement effect of ultrathin protective silica layers stabilizes ultrasmall Pd nanoclusters and impedes the agglomeration and sintering of ultrasmall Pd nanoclusters during electrocatalysis. As a result, the ultrasmall Pd nanoclusters (∼1.4 nm) confined in silica layers on NrGO (Pd/NrGO@SiO2) demonstrate a very high forward peak current density for formic acid oxidation (FAO) of 2.37 A mg-1, outperforming the Pd/C catalyst (0.30 A mg-1) and the Pd/rGO catalyst obtained by a conventional method (0.42 A mg-1). More importantly, our confined Pd catalysts show the highest stability of only 5% inconspicuous degradation of the initial mass activity after 1000 cycles, compared with Pd/C (almost 100% loss), Pd/rGO (61.5% loss) and Pd/NrGO (73.2% loss). These strategies in this work provide a new prospect for the design of excellent noble catalysts to overcome the challenges in the practical application of DFAFCs.

Simple synthesis of hierarchically porous Sn/TiO2/graphitic carbon microspheres for CO2 reduction with H2O under simulated solar irradiation

A simple colloidal crystal template method was used to prepare Sn/TiO₂/graphite carbon microsphere composites (xSn/TiO₂/GCM, x = 2.0, 1.0, 0.2, 0.5) with porous layers. Then, the composites were represented using X-ray diffraction, energy dispersive spectrometry, scanning electron microscopy, transmission electron microscopy, and nitrogen physical adsorption/desorption. Meanwhile, the photocatalytic activities in CO₂ reduction were studied under simulation of visible light exposure. It was confirmed that the Sn/TiO₂/GCM composites had layered porosity, graphitized carbon matrix, and high metal compound content, and their morphology was greatly affected by the acetone amount. The outputs of CO and CH₄ coming into the photocatalytic CO₂ reduction reaction of Sn/TiO₂/GCM were 619.46 and 14.46 μmol g^-1, respectively. Among the two products, the highest production rate observed in 0.5Sn/TiO₂/GCM. Because of these factors, the layered porous Sn/TiO₂/GCM composites have good photocatalytic performance under simulated visible light irradiation and have unique composition and structure characteristics, which give broad application prospects in electrode materials, catalysts, and adsorbents. Graphical abstract.

Highly Stable Reduced Graphene Oxide Wrapped Black Phosphorus Heterostructure with Superior Photocatalytic Performance under Visible Light

Metal-free photocatalysts with excellent visible-light absorption and highly efficient photocatalytic activity are attractive in the field of photocatalysis owing to their environmental friendliness. Black phosphorus (BP) shows a great potential in photoelectric conversion and photocatalysis due to its tunable band gap and two-dimensional structure. In this work, a stabilized metal-free photocatalyst, reduced graphene oxide (rGO)-wrapped BP heterostructure, was prepared by assembling BP and GO nanosheets in aqueous solution followed by partial reduction and lyophilization. The surface tension of the partially reduced GO during lyophilization could make rGO nanosheets tightly wrap on both surfaces of exfoliated BP nanosheets. This wrapped heterostructure with tight bonding between rGO and BP nanosheets led to a high photocatalytic activity, owing to the rapid transfer of the photogenerated electron-hole pairs at the rGO/BP heterojunction and the high stability of rGO protecting BP from oxygen attack. This work not only provided a general method to prepare the sandwiched heterojunction based on GO with good interface binding capability but also constructed a highly active, stable, metal-free photocatalyst based on BP.

Tunable long-chains of core@shell PdAg@Pd as high-performance catalysts for ethanol oxidation

High performance nanomaterial catalysts have attracted great attention on the application for the direct alcohol fuel cell. To improve the catalytic behavior, it is a challenge to modulate the surface structure and morphology of catalysts. We integrated properties of advanced networks nanostructure and core@shell structure to form a series of PdAg@Pd worm-like networks catalysts. Importantly, the composition-optimized Pd₇₆Ag₂₄ WNWs exhibited excellent catalytic performance towards ethanol oxidation reaction compared to that of commercial Pd/C catalysts in alkaline media. The mass activity of Pd₇₆Ag₂₄ WNWs is 3.55 times higher than that of commercial Pd/C catalysts for EOR. Moreover, the Pd₇₆Ag₂₄ WNWs also showed superior stability after 250 successive cycles and kept far higher residual activities than that of the other catalysts. The synthesis of PdAg@Pd worm-like networks catalysts provides a reference to well combine the advantages of core@shell and networks structure to form high performance catalysts application for DEFC.

Catalysis Mediated by 2D Black Phosphorus Either Pristine or Decorated with Transition Metals Species

Among the novel class of mono-elemental two-dimensional (2D) materials, termed Xenes, phosphorene is emerging as a great promise for its peculiar chemical and physical properties. This review collects a selection of the recent breakthroughs that are related to the application of phosphorene in catalysis and electrocatalysis. Noteworthy, thanks to its intrinsic Lewis basic character, pristine phosphorene turned out to be more efficient and more selective than other non-metal catalysts, in chemical processes as the electroreduction of nitrogen to ammonia or the alkylation of nucleophiles with esters. Once functionalized with transition metals nanoparticles (Co, Ni, Pd, Pt, Ag, Au), its catalytic activity has been evaluated in several processes, mainly hydrogen and oxygen evolution reactions. Under visible light irradiation, it has shown a great improvement of the activity, demonstrating high potential as a photocatalyst.

Ir3Pb alloy nanodendrites with high performance for ethanol electrooxidation and their enhanced durability by alloying trace Au

Porous Ir₃Pb nanodendrites exhibit excellent activity and superior CO₂ selectivity for the EOR under acidic conditions, and their durability can be enhanced dramatically by alloying trace Au.

Boosting the electrocatalytic activity of amorphous molybdenum sulfide nanoflakes via nickel sulfide decoration

As a coordination polymer built of [Mo₃S₁₃]^2- clusters, amorphous nanoscale MoS_x (a-MoS_x) is an attractive electrocatalyst for the hydrogen evolution reaction (HER) due to its abundant active sites and scalable synthesis. However, clarifying the internal catalytic mechanism and achieving even higher HER performance with scalable size are still challenging. Herein, a new hybrid catalyst of a-MoS_x flakes decorated with Ni₃S₂ nanocrystals (size < 10 nm) has been successfully synthesized on 10 × 20 cm²-sized Ni foam by a portable hydrothermal route. As the strong interaction of [Mo₃S₁₃]^2- clusters with Ni₃S₂ is evidenced by comprehensive binding state and Raman characterization, the polymerization effect of [Mo₃S₁₃]^2- itself and the perfect interfaces between [Mo₃S₁₃]^2- clusters and Ni₃S₂ are also confirmed by density functional theory calculations. These two factors greatly lower the absorption energy of hydrogen nearly to zero, leading to much improved HER activity. Current densities of 100 and 600 mA cm^-2 are achieved at overpotentials of 181 and 246 mV, respectively, which are so far the highest values approaching practical applications. The findings of this work provide a fundamental reference about the catalytic origin of a-MoS_x based catalysts, and shed light on the practical applications of non-precious electrocatalysts for their compatibility with low cost batch production.

Trimetallic palladium-copper-cobalt alloy wavy nanowires improve ethanol electrooxidation in alkaline medium

Recently, engineering high performance Pd-based nanocatalysts for alkaline ethanol fuel cells has attracted wide attention. Here, we report a one-pot synthesis of low-palladium ternary palladium-copper-cobalt (PdCuCo) alloy nanowires (NWs) with a diameter of ∼4.0 nm to improve the mass activity (MA) of ethanol electrooxidation in alkaline medium. The MA (7.45 A mg^-1) of the Pd₃₁Cu₆₁Co₈ NWs is 8.5-fold and 12.4-fold that of commercial Pd black and Pd/C, respectively. The reaction mechanism of the EOR and the reasons for the activity enhancement on Pd₃₁Cu₆₁Co₈ NWs are elucidated based on the results of in situ Fourier transform infrared spectroscopy and structure characterization. Besides the electronic effect and surface defect sites, the coexistence of surface Cu and Co that have high capacities to activate water to produce reactive oxygen species is another key factor. This study shows an example of how to design low-palladium ternary PdCuCo NWs as improved anode electrocatalysts for alkaline direct ethanol fuel cells with high mass activity.

Nickel Nitride Particles Supported on 2D Activated Graphene-Black Phosphorus Heterostructure: An Efficient Electrocatalyst for the Oxygen Evolution Reaction

Hydrogen is regarded as the most promising green clean energy in the 21st century. Developing the highly efficient and low-cost electrocatalysts for oxygen evolution reaction (OER) is of great concern for the hydrogen industry. In the water electrolyzed reaction, the overpotential and the kinetics are the main hurdles for OER. Therefore, an efficient and durable oxygen evolution reaction electrocatalyst is required. In this study, an activated graphene (AG)-black phosphorus (BP) nanosheets hybrid is fabricated for supporting Ni₃ N particles (Ni₃ N/BP-AG) in the application of OER. The Ni₃ N particles are combined with the BP-AG heterostructure via facile mechanical ball milling under argon protection. The synthesized Ni₃ N/BP-AG shows excellent catalytic performance toward the OER, demanding the overpotential of 233 mV for a current density of 10 mA cm^-2 with a Tafel slope of 42 mV dec^-1 . The Ni₃ N/BP-AG catalysts also show remarkable stability with a retention rate of the current density of about 86.4% after measuring for 10 000 s in potentiostatic mode.

Plasma-modified Ti3C2Tx/CdS hybrids with oxygen-containing groups for high-efficiency photocatalytic hydrogen production

Noble-metal-free Ti₃C₂T_x/CdS hybrids with oxygen-containing groups were successfully prepared through a mild solvothermal method of in situ heterogeneous nucleation. The abundant oxygen-containing groups and the increased surface roughness of plasma-treated Ti₃C₂T_x sheets provided active sites for the heterogeneous nucleation of CdS nanoparticles and strengthened the physical bond between CdS NPs and layered Ti₃C₂T_x. The optimized Ti₃C₂T_x/CdS hybrid without noble-metal co-catalyst achieved a high hydrogen-production rate of 825 μmol h^-1 g^-1 with an apparent quantum efficiency of 10.2% at 450 nm. The prepared Ti₃C₂T_x/CdS hybrid with 1.0 wt% Ti₃C₂T_x had a photocatalytic hydrogen-production rate higher than those of pure CdS nanoparticles and the Ti₃C₂/CdS hybrid obtained using non-plasma-treated Ti₃C₂ as the support matrix under visible-light irradiation. The photocatalytic-activity improvement of CdS nanoparticles was due to the increased hydrophilicity after plasma treatment with the abundant oxygen-containing groups on the Ti₃C₂T_x surface and the intimate contact between CdS nanoparticles and layered Ti₃C₂T_x. The former enabled the effective capture of water molecules and hydrogen ions by oxygen-containing groups on the surface of plasma-treated Ti₃C₂T_x. The latter provided a stable transfer channel for electrons to suppress the recombination of photogenerated electron-hole pairs. The proposed schematic for the improved photocatalytic activity of CdS nanoparticles decorated with plasma treated Ti₃C₂T_x was further confirmed by transient photocurrent response and time-resolved photoluminescence analyses.

Simple Preparation of Hierarchically Porous Ce/TiO2/Graphitic Carbon Microspheres for the Reduction of CO2 with H2O under Simulated Solar Irradiation

Hierarchically porous Ce/TiO2/graphitic carbon microsphere composites (xCe/TiO2/GCM, where x = 0.2, 1.0, 2.0, 5.0 mmol·L-1) were prepared for the first time by using a simple colloidal crystal template and characterized by X-ray diffraction, nitrogen adsorption and desorption, scanning electron microscopy, and ultraviolet-visible diffuse reflectance spectra. In addition, the photocatalytic activity of CO2 reduction by H2O under simulated solar irradiation was studied. The results showed that the Ce/TiO2/GCM composite material was characterized by large porosity, high concentration of metal compounds and graphitized carbon matrix, and the content of acetone solvent having a great impact on its form. In terms of the photocatalytic CO2 reaction, the CH4 and CO productions were 4.587 and 357.851 μmol·g-1, respectively. The 2Ce/TiO2/GCM photocatalyst gave the highest production rate for three products. Under simulated solar irradiation, the Ce/TiO2/GCM has excellent photocatalytic activity in the photoreduction of CO2 from H2O, which was related to the special composition and the Ce/TiO2/GCM structure.