Black Phosphorus-Modified Co3O4 through Tuning the Electronic Structure for Enhanced Oxygen Evolution Reaction

Two-dimensional confined topotactic transformation to produce Co-Pi/Co3O4 hybrid porous nanosheets for promoted water oxidation

Exploring advanced electrocatalyst for the oxygen evolution reaction (OER) is of great importance in pursuing efficient and sustainable hydrogen production via electrolytic water splitting. Considering the structure-activity-stability relationship for designing advanced OER catalysts, two-dimensional (2D) porous catalyst with single crystallinity is deemed to be an ideal platform which could simultaneously endow enriched active sites, facile mass and charge transport ability as well as robust structural stability. Herein, we proposed a facile 2D confined topotactic phase transformation approach, which realizes the fabrication of highly porous single-crystalline Co3O4 nanosheets with in-situ surface modification of amorphous Co-Pi active species. Benefitted from the highly exposed undercoordinated cobalt sites, facilitated mass transport and facile 2D charge transfer pathway, the Co-Pi/Co3O4 hybrid porous nanosheets display enhanced OER activity with obvious pre-oxidation-induced activation. In addition, the operational stability was significantly improved owing to the strengthened structural stability which effectively buffers the internal strains and avoids the structural collapse during the electrochemical process. This work proposed a facile and mild method for the synthesis of amorphous/single-crystalline hybrid porous materials, and the achievement of synergistic modulation of active site density and charge transfer ability via targeted microstructural construction will shed light on catalyst design in the future.

Core-bishell NiFe@NC@MoS2 for boosting electrocatalytic activity towards ultra-efficient oxygen evolution reaction

Designing and developing suitable oxygen evolution reaction (OER) catalysts with high activity and stability remain challenging in electrolytic water splitting. Hence, NiFe@NC@MoS2 core-bishell composites wrapped by molybdenum disulphide (MoS2) and nitrogen-doped graphene (NC) were prepared using hydrothermal synthesis in this research. NiFe@NC@MoS2 composite exhibits excellent performance with an overpotential of 288 mV and a Tafel slope of 53.2 mV·dec-1 at a current density of 10 mA·cm-2 in 1 M KOH solution, which is superior to commercial RuO2. NC and MoS2 bishells create profuse edge active sites that enhance the adsorption ability of OOH* while lowering the overall overpotential of the product and improving its oxygen precipitation performance. The density function theory(DFT) analysis confirms that the layered MoS2 in NiFe@NC@MoS2 provides additional edge active sites and enhances electron transfer, thus increasing the intrinsic catalytic activity. This research paves a novel way for developing OER electrocatalysts with excellent catalytic performance.

Enhanced Catalytic Activity of Crystalline Phosphorus Nanosheets Fabricated via Solvothermal Phase Transformation

The newly reported crystalline phosphorus nanosheets (cryst-P NSs) exhibit promising features for industrial applications, including outstanding air-water stability and facile large-scale production. However, their complex crystallization impedes a priori tailoring. Herein, the temporal evolution of cryst-P NSs was investigated with the optimized synthesis parameters. The occurrence of self-assembly and solid-state rearrangement unveiled the existence of an intermediate phase as the bulk crystalline precursor and the predominance of nonclassical crystallization pathway(s). With the upgraded synthesis protocol simultaneously strengthening the merits of cryst-P NSs, their catalytic performances were evaluated in various electro- and/or photocatalytic reactions spanning hydrogen and oxygen evolution, full water splitting, CO2 reduction, and organic pollutant decomposition. Superior catalytic activities and orders of magnitude longer lifetimes were consistently discerned compared with the widely employed black phosphorus nanosheets with similar size and thickness. The exciting discoveries in both fundamental crystallization and catalytic applications drastically thrust the comprehension of elemental phosphorus, shedding light on the encouraging capabilities of solvothermal synthesis strategies in the design and systematic tailoring of phosphorus materials.

Experimental and Theoretical Insights of Anion Regulation in MOF-Derived Ni-Co-Based Nanosheets for Supercapacitors and Anion Exchange Membrane Water Electrolyzers

The anionic components have a significant role in regulating the electrochemical properties of mixed transition-metal (MTM)-based materials. However, the relationship between the anionic components and their inherent electrochemical properties in MTM-based materials is still unclear. Herein, we report the anion-dependent supercapacitive and oxygen evolution reaction (OER) properties of in situ grown binary Ni-Co-selenide (Se)/sulfide (S)/phosphide (P) nanosheet arrays (NAs) over nickel foam starting from MOF-derived Ni-Co layered double hydroxide precursors. Among them, the Ni-Co-Se NAs exhibited the best specific capacity (289.6 mA h g^-1 at 4 mA cm^-2). Furthermore, a hybrid device constructed with Ni-Co-Se NAs delivered an excellent energy density (74 W h kg^-1 at 525 W kg^-1) and an ultra-high power density (10 832 W kg^-1 at 46 W h kg^-1) with outstanding durability (∼94%) for 10 000 cycles. Meanwhile, the Ni-Co-Se NAs showed superior electrocatalytic OER outputs with the lowest overpotential (235 mV at 10 mA cm^-2) and Tafel slope. In addition, Ni-Co-Se NAs outperformed IrO₂ as an anode in an anion exchange membrane water electrolyzer at a high current density (>1.0 A cm^-2) and exhibited a stable performance up to 48 h with a 99% Faraday efficiency. Theoretical analyses validate that the Se promotes OH adsorption and improves the electrochemical activity of the Ni-Co-Se through a strong electronic redistribution/hybridization with an active metal center due to its valence 4p and inner 3d orbital participations. This study will provide in-depth knowledge of bifunctional activities in MTM-based materials with different anionic substitutions.

Strong Electronic Orbit Coupling between Cobalt and Single-Atom Praseodymium for Boosted Nitrous Oxide Decomposition on Co3O4 Catalyst

Nitrous oxide (N₂O) has gained increasing attention as an important noncarbon dioxide greenhouse gas, and catalytic decomposition is an effective method of reducing its emissions. Here, Co₃O₄ was synthesized by the sol-gel method and single-atom Pr was confined in its matrix to improve the N₂O decomposition performance. It was observed that the reaction rate varied in a volcano-like pattern with the amount of doped Pr. A N₂O decomposition reaction rate 5-7.5 times greater than that of pure Co₃O₄ is achieved on the catalyst with a Pr/Co molar ratio of 0.06:1, and further Pr doping reduced the activity due to PrO_x cluster formation. Combined with X-ray photoelectron spectroscopy, X-ray absorption fine structure, density functional theory and in situ near-ambient pressure X-ray photoelectron spectroscopy, it was demonstrated that the single-atom doped Pr in Co₃O₄ generates the "Pr 4f-O 2p-Co 3d" network, which redistributes the electrons in Co₃O₄ lattice and increases the t_2g electrons at the tetracoordinated Co²⁺ sites. This coupling between the Pr 4f orbit and Co²⁺ 3d orbit triggers the formation of a 4f-3d electronic ladder, which accelerates the electron transfer from Co²⁺ to the 3π* antibonding orbital of N₂O, thus contributing to the N-O bond cleavage. Moreover, the energy barrier for each elementary reaction in the decomposition process of N₂O is reduced, especially for O₂ desorption. Our work provides a theoretical grounding and reference for designing atomically modified catalysts for N₂O decomposition.

Mn2+ modified black phosphorus nanosheets with enhanced DNA adsorption and affinity for robust sensing

To develop various biosensors, several 2D nanomaterials adsorb DNA probes (aptamers) via π-π stacking interactions. However, interference from DNA displacement by external non-targeted ligands has precluded their practical applications for specific detection and imaging at high protein concentrations. Metal coordination is an attractive strategy for biomolecular crosslinking and functional molecular self-assembly. Herein, a robust 2D biosensor nanoplatform was developed to enhance DNA adsorption and affinity using Mn²⁺-modified black phosphorus nanosheets (BPNS@Mn²⁺) via metal coordination. The Mn²⁺ can simultaneously coordinate with the lone pair electrons (π bonds) of the BPNS and nucleotide bases to provide binding sites for DNA nucleobases on the BPNS surface, which greatly enhances the stability of the inner BPNS and improves DNA adsorption and affinity. The DNA adsorption mechanism of BPNS@Mn²⁺ was also characterized, and is extensively discussed. Without any further modification, this BPNS@Mn²⁺/DNA biosensor specifically detected single-stranded DNA (linear range: 10-200 nM, detection limit: 5.76 nM) and thrombin (linear range: 20-180 nM, detection limit: 2.39 nM) in 100 nM bovine serum albumin solution. The nonspecific ligands in the environment did not affect the detection performance of the robust biosensor. In addition, the expression levels of microRNA-21 can be imaged and analyzed in living cells using this biosensor, which is consistent with the results of the polymerase chain reaction. This study highlights the potential of metal coordination in surface modification and provides new opportunities for biomedical applications of 2D nanomaterials with superior DNA-adsorption capacity, facilitating the development of biosensor design and nucleic acid/drug delivery.

Nanomaterial-enabled photothermal-based solar water disinfection processes: Fundamentals, recent advances, and mechanisms

The pathogenic microorganisms in water pose a great threat to human health. Photothermal and photothermocatalytic disinfection using nanomaterials (NPs) has offered a promising and effective strategy to address the challenges in solar water disinfection (SODIS), especially in the point-of-use operations. This review aims at providing comprehensive and state-of-the-art knowledge of photothermal-based disinfection by NPs. The fundamentals and principles of photothermal-based disinfection were first introduced. Then, recent advances in developing photothermal/photothermocatalytic catalysts were systematically summarized. The light-to-heat conversion and disinfection performance of a large variety of photothermal materials were presented. Given the complicated mechanisms of photothermal-based disinfection, the attacks from reactive oxygen species and heat, the destruction of bacterial cells, and the antibacterial effects of released metal ions were highlighted. Finally, future challenges and opportunities associated with the development of cost-effective photothermal/photothermocatalytic disinfection systems were outlined. This review will provide guidance in designing future NPs and inspire more research efforts from environmental nano-communities to move towards practical water disinfection operations.

Ag decoration-enabled sensitization enhancement of black phosphorus nanosheets for trace NO2 detection at room temperature

Black phosphorus (BP), one rising star of two-dimensional (2D) materials, has showcased a huge capability for ppb-level NO₂ detection. However, sluggish reaction kinetics and fragile stability frustrate its further application. In this regard, for the first time we prepared Ag nanoparticles modified BP nanosheets as the sensing layer via one feasible method to recognize trace NO₂ at room temperature. With respect to individual BP, the composition-optimized BP-Ag nanocomposites (BP-Ag-1 sensor) achieved a favorable performance primarily in terms of boosted response (39.9% vs. 11.8%, 100 ppb NO₂), accelerated response speed (190 s vs. 486 s, 100 ppb NO₂) and strengthened operation stability, together with ultralow theoretical detection limit of 0.25 ppb. Furthermore, a protection layer comprised of polylactic acid (PLA) was anchored onto the surface of BP-Ag-1 sensor to keep the water molecules physically from the sensing layer and retain a distinguishable signal toward trace NO₂ at high moisture environments. The introduction of Ag and PLA separately reduced the lone electron pairs from P atoms and suppressed the water penetration into the BP film, thereby offering an alternative way to passivate BP for its optoelectronic applications in the future.

Sandwiching Phosphorene with Iron Porphyrin Monolayer for High Stability and Its Biomimetic Sensor to Sensitively Detect Living Cell Released NO

Instability of 2D phosphorene material is the major obstacle for its broad applications. Herein phosphorene is sandwiched with self-assembled iron porphyrin monolayers on both sides (I-Phene) to significantly enhance stability. Iron porphyrin has strong interaction with phosphorene through formation of PFe bonds. The sandwich structure offers excellent stability of phosphorene by both-sided monolayer protections for an intact phosphorene structure more than 40 days under ambient conditions. Meanwhile, the electron transfer between iron porphyrin and phosphorene result in a high oxidation state of Fe, making I-Phene biomimetic sensitivity toward oxidation of nitric oxide (NO) for 2.5 and 4.0 times higher than phosphorene and iron-porphyrin alone, respectively. Moreover, I-Phene exhibits excellent selectivity, a wide detection range, and a low detection limit at a low oxidation potential of 0.82 V, which is comparable with the reported noble metal based biomimetic sensors while ranking the best among all non-noble biomimetic ones. I-Phene is further used for real-time monitoring NO released from cells. This work provides effective approach against phosphorene degrading for outstanding stability, which has universal significance for its various important applications, and holds a great promise for a highly sensitive biomimetic sensor in live-cell assays.

Site dependent catalytic water dissociation on an anisotropic buckled black phosphorus surface

Black phosphorus (BP) is unique among 2D materials due to its anisotropic puckered structure. It has been used as a multifunctional catalyst for various purposes. In this study, we performed first principles molecular dynamics simulations to understand the water-splitting reaction on a bi-layer BP surface. We focused on the site-specific aqueous reactivity of the buckled surface. A difference in the axis-dependent reactivity is observed owing to edge defects and exposed sites. Thus, we believe that BP edges, which significantly affect the interfacial water or organic solvent molecules, must exhibit very different edge-dependent reactivity. Experiments suggested the increasing catalytic efficiency of undisturbed BP in the order bulk, few-layered BP, and BP quantum dots. We choose three active sites to investigate the mechanistic details of the OER: the zigzag (ZZ), armchair (AC), and bulk sites. This study will provide insight into the enhanced catalytic activity when more edges are exposed as the active surface. We hope to clarify the reactive pathway in an aqueous solution supported by bi-layer BP by exploring the two different mechanisms for forming the OOH* complex. We explore and report two mechanisms: a simple push-pull reaction for oxygen-oxygen bond formation, the nucleophilic attack by formed OH^- and an attack by a water molecule. The free energy barriers procured for mechanism 1 taking place at the zigzag, armchair, and bulk sites are 7.59 ± 0.33, 9.04 ± 0.01, and 12.80 ± 0.09 kcal mol^-1, respectively. For mechanism 2 the free energy barriers are 7.62 ± 0.11, 9.15 ± 0.16, and 11.63 ± 0.11 kcal mol^-1 for the ZZ, AC, and bulk sites. The interlink between both the mechanisms is established concerning the reported free energy barriers for OOH* formation. The ZZ site is found to lower the activation barrier for the rate-determining step, followed by the AC and bulk.

Regulating oxygen vacancies in Co3O4by combining solution reduction and Ni2+ impregnation for oxygen evolution reaction

Oxygen vacancies are considered to be an important factor to influence the electronic structure and charge transport of electrocatalysts in the field of energy chemistry. Various strategies focused on oxygen vacancy engineering are proved to be efficient for further improving the electrocatalytic performance of Co₃O₄. Herein, an optimal Co₃O₄with rich oxygen vacancies have been synthesized via a two-step process combining solution reduction and Ni²⁺impregnation. The as-prepared electrocatalyst exhibits an enhanced oxygen evolution performance with the overpotential of 330 mV at the current density of 10 mA cm^-2in alkaline condition, which is 84 mV lower than that of pristine one. With the increasing of oxygen vacancies, the charge transfer efficiency and surface active area are relatively enhanced reflected by the Tafel slope and double-layer capacitance measurement. These results indicate that combination of solution reduction and heteroatom doping can be a valid way for efficient metal oxides-based electrocatalyst development by constructing higher concentration of oxygen vacancy.

Cobalt-Nickel Phosphate Composites for the All-Phosphate Asymmetric Supercapacitor and Oxygen Evolution Reaction

Recently, design of cost-effective multifunctional electromaterials for supercapacitors and oxygen evolution reaction (OER) and enhancing their functionalities have become an emphasis in energy storage and conversion. Herein, a series of cheap and functional phosphate composites with different ratios of cobalt and nickel are synthesized using a simple polyalcohol refluxing method, and their excellent capacity and OER properties are systematically studied. Notably, owing to the different major role of Co and Ni elements in the phosphate composites for capacity and OER, the optimal electroconductibility, structural adjustment, electrochemical active sites, and activities for capacity and OER are obtained from the composites with the different ratios of Co/Ni. In addition, using high-capacity BiPO₄ (BPO) as the negative electrodes, the new type of all-phosphate asymmetric supercapacitor (CNPO-40//BPO) shows a high energy density and reaches 36.84 W h kg^-1 at a power density of 254.52 W kg^-1. Its cyclic stability is also more excellent than that of the CNPO-40//AC device using commercial activated carbon as the negative electrodes. This study is beneficial to the more in-depth research on efficient dual-function electromaterials in capacity and OER and provides a high-efficient way to improve the practicality of asymmetric supercapacitors using the high-capacity Bi-based electromaterials as the negative electrodes.

2D Heterostructure of Amorphous CoFeB Coating Black Phosphorus Nanosheets with Optimal Oxygen Intermediate Absorption for Improved Electrocatalytic Water Oxidation

The oxygen evolution reaction (OER) plays a paramount role in a variety of electrochemical energy conversion devices, and the exploration of highly active, stable, and low-cost electrocatalysts is one of the most important topics in this field. The exfoliated black phosphorus (EBP) nanosheet with a two-dimensional (2D) layered structure has high carrier mobility but is limited by excessive oxygen-containing intermediate absorption and fast deterioration in air. We here report the fabrication of nanohybrids of amorphous CoFeB nanosheets on EBP nanosheets (EBP/CoFeB). The 2D/2D heterostructure, thanks to the electronic interactions and oxygen affinity difference between EBP and CoFeB nanosheets, is capable of balancing the oxygen-containing intermediate absorption to an optimal status for facilitating the OER process. While the crystalline EBP contributes to the improved conductivity, the amorphous coating protects EBP and thus ensures the catalytic stability. The EBP/CoFeB electrocatalyst shows excellent OER performance with an ultralow overpotential of 227 mV at 10 mA cm^-2 with an ultrasmall Tafel slope of 36.7 mV dec^-1 with excellent stability. This study may inspire more researches to develop heterostructured nanohybrid electrocatalysts for a diversity of electrochemical reactions.

Constructed Interfacial Oxygen-Bridge Chemical Bonding in Core-Shell Transition Metal Phosphides/Carbon Hybrid Boosting Oxygen Evolution Reaction

A designed structure which CoP nanoparticles (NPs) ingeniously connected with graphene-like carbon layer via in-situ generated interfacial oxygen-bridge chemical bonding was achieved by a mild phosphorization treatment. The results proved that the presence of phosphorus vacancies is a crucial factor enabling formation of Co-O-C bonds. The direct coupling of edge Co of CoP with the oxygen from functional groups on the carbon layer was proposed. As a catalyst for electrocatalytic water splitting, the manufactured Fe₂ O₃ @C@CoP core-shell structure manifested a low overpotential of 230 mV, a low Tafel slope of 55 mV dec^-1 , and long-term stability. Density functional theory calculations verified that the Co-O-C bond played a critical role in decreasing the thermodynamic energy barrier of reaction rate-determining step for the oxygen evolution reaction (OER). This synthetic route might be extended to construct metal-O-C bonds in other transition metal phosphides (or selenides, sulfides)/carbon composites for highly efficient OER catalysts.

High-Quality CoFeP Nanocrystal/N, P Dual-Doped Carbon Composite as a Novel Bifunctional Electrocatalyst for Rechargeable Zn-Air Battery

A novel composite catalyst (CoFeP@C) was constructed by high-quality CoFeP nanoparticles embedded in a N, P dual-doped carbon matrix. These CoFeP nanoparticles are rich in active sites of the oxygen evolution reaction (OER) at surfaces and provide metallic conductivity in their bulk phases. The N, P dual-doped carbon matrix provided abundant active sites of the oxygen reduction reaction (ORR) and formed a conductive network substrate. The ideal composite structure endowed CoFeP@C with highly efficient bifunctional performance for catalyzing both OER and ORR, accordingly making CoFeP@C an ideal catalyst for rechargeable Zn-air batteries. The liquid Zn-air battery of CoFeP@C has achieved a large power density of 143.5 mW/cm² and can be charged and discharged stably for 200 h (1200 cycles). The solid-state Zn-air battery of CoFeP@C has achieved a power density of 72.6 mW/cm² and can stably run for 20 h. This work has deepened the understanding of synergistic catalysis and paved one way for the development of high-performance bifunctional catalysts.

Structural dependence of electrosynthesized cobalt phosphide/black phosphorus pre-catalyst for oxygen evolution in alkaline media

The integration of black phosphorus (BP) with metal phosphides is known to produce high-performance electrocatalysts for oxygen evolution reduction (OER), although increased stability and prevention of the degradation of their lone pairs would be desirable improvements. In this work, cobalt phosphide (CoP)/BP heterostructures were electrochemically synthesized with a two-electrode system, where cobalt ions were generated in situ at a Co anode, and non-aggregated BP nanosheets (NSs) were exfoliated from the bulky BP cathode. With an electrolysis voltage of 30 V, the CoP/BP heterostructure exhibited a superior and stable OER performance (e.g., an overpotential of 300 mV at 10 mA cm^-2, which is 41 mV lower than that obtained with a RuO₂ catalyst). The CoO_x formed in situ during the OER catalysis and remaining CoP synergistically contributed to the enhanced OER performance. The present strategy provides a new electrosynthetic method to prepare stable BP electrocatalysts and also further expands their electrochemical applications.

Donor-Acceptor Couples of Metal and Metal Oxides with Enriched Ni3+ Active Sites for Oxygen Evolution

Exploiting precious-metal-free and high-activity oxygen evolution reaction (OER) electrocatalysts has been in great demands toward many energy storage and conversion processes, for example, carbon dioxide reduction, metal-air batteries, and water splitting. In this study, the simple solid-state method is employed for coupling Ni (electron donors) with lower-Fermi-level MoO₂ or WO_x (electron acceptors) into donor-acceptor ensembles with well-designed interfaces as robust electrocatalysts for OER. The resulting Ni/MoO₂ and Ni/WO_x electrocatalysts exhibit smaller overpotentials of 287 and 333 mV at 10 mA cm^-2 as well as smaller Tafel slopes of 51 and 65 mV/dec, respectively, with respect to the single Ni, MoO₂, WO_x, and even the benchmark RuO₂ in 1 M KOH. Specially, on account of a higher Fermi level of Ni in comparison with MoO₂ and WO_x, their strong electronic interaction results in directional interfacial electron transfer and increases the hole density over Ni, dramatically enriching the population of high-valence Ni³⁺ active sites and decreasing the Fermi level of Ni. The existence of Ni³⁺ can strengthen the chemisorption of OH^-, and the downshift of the Ni Fermi level can significantly expedite migration of electrons toward the surface of catalysts during OER, thus synergistically boosting the OER catalytic performance. Furthermore, the inner Ni/MoO₂ and Ni/WO_x heterostructures and the electrochemically induced surface layers of oxides/hydroxides collectively boost the OER kinetics. This study highlights the importance of designing highly efficient OER electrocatalysts with high-valence active species (Ni³⁺) and better matched energy levels induced by the work function difference through interfacial engineering.

A ternary hybrid of Zn-doped MoS2-RGO for highly effective electrocatalytic hydrogen evolution

Modification of MoS₂-based catalysts is effective in solving the overdependence of hydrogen evolution reactions (HERs) on noble metal catalysts. In this work, a Zn-doped molybdenum disulfide-reduced graphene oxide (Zn-MoS₂-RGO) hybrid was synthesized in one step employing a hydrothermal method. By substituting the position of Mo, uniform doping with Zn improved the catalytic activity of MoS₂ for HER. The interlayer spacing of MoS₂ increased from 0.65 to 0.75 nm, demonstrating RGO effectively interpolate into MoS₂ nanosheets. This prevented aggregation and exposed more edge active sites of MoS₂. According to density functional theory (DFT) calculations, the layered structure of the MoS₂ nanosheets doped with Zn and intercalated with RGO promoted charge transfer and resulted in outstanding hydrogen evolution activity. Compared with MoS₂ (6.86 eV), the Zn-MoS₂-RGO hybrid (5.47 eV) with a considerably lower energy level value exhibited excellent electrocatalytic performance. Under optimal conditions, at a potential of -0.3 V vs. RHE, the current density reached -169 mA cm^-2 in a 0.5 M H₂SO₄ solution, 4.78 μmol of H₂ was produced in 6 h, and the Faraday efficiency reached 92%. The results obtained herein indicated that Zn-MoS₂-RGO was a promising candidate for application in electrocatalytic HER.

The thermodynamics and electronic structure analysis of P-doped spinel Co3O4

The thermodynamics of phosphorus (P) doping to spinel Co₃O₄, for both bulk cases and (100) and (110) surface cases, is studied using first principles calculations. The doping energies of the P atom at different doping sites are carefully calculated and compared. It is shown that P doping at Co sites, at either tetrahedral or octahedral sites, is energetically favorable, while P doping and replacing O atoms are energetically unfavorable. The doping energy difference is large enough to conclude that P doping has a very strong preference to take the Co sites, rather than the O sites in spinel Co₃O₄. Even when O-vacancy is available, P doping and taking the O-vacancy site is thermodynamically unfavorable. The physical/chemical mechanism behind this phenomenon is carefully analyzed. Electronic structure analysis shows that P doping and replacing the Co atom brings excess electrons to the Co₃O₄ system, which is beneficial to enhance the electrochemical and catalytic performance of the spinel Co₃O₄. Our results clarified the misleading results of P doping and replacing O atoms in spinel Co₃O₄ reported in the literature.

Hard template synthesis of 2D porous Co3O4 nanosheets with graphene oxide for H2O2 sensing

In this work, we used graphene oxide (GO) as a template that was removed by calcination to finally successfully prepare Co₃O₄ with 2D porous nanostructure. The results show that 2D porous structure Co₃O₄ nanosheets were only prepared at pH = 2. After electrochemical tests, the as-prepared Co₃O₄ nanosheets showed electrochemical properties that are highly suitable for H₂O₂ detection, such as high current response, short response time (less than 3 s), wide linear range (0.388-44.156 mM), low limit of detection (2.33 μM) and high sensitivity (0.0891 mA mM^-1 cm^-2). These excellent properties are mainly due to GO, as a 2D template, which connects Co₃O₄ nanoparticles to each other on a 2D plane, preventing the agglomeration of Co₃O₄ nanoparticles. The abundant pores between Co₃O₄ nanoparticles can greatly increase the reaction between the nanoparticles and H₂O₂ molecules.

Tuning W18O49/Cu2O{111} Interfaces for the Highly Selective CO2 Photocatalytic Conversion to CH4

As a multiple proton-coupled electron transfer process, photocatalytic conversion of CO₂ usually produces a wide variety of products. Improving the yield and selectivity of CO₂ to the single product is still a significant challenge. In this work, we describe that the rationally constructed W₁₈O₄₉/Cu₂O{111} interfaces achieve highly selective CO₂ photocatalytic conversion to CH₄. In situ Fourier transform infrared spectroscopy measurements reveal that the formation of W₁₈O₄₉/Cu₂O{111} interfaces restrains the desorption of CO* intermediates in CO₂ photocatalytic conversion. UPS spectra, PL spectra, and photocurrent curves show that more photogenerated electrons are excited and transferred to W₁₈O₄₉/Cu₂O{111} interfaces. All of these play critical roles in CH₄ production. As an outcome, the yield rate of CO₂ photocatalytic conversion to CH₄ was enhanced from 6.5 to 17.20 μmol g^-1 h^-1 with selectivity as high as 94.7%. The work demonstrates the feasibility and versatility of interface engineering in achieving highly selective CO₂ photocatalytic conversion.

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.

Recent Advances in Chemical Functionalization of 2D Black Phosphorous Nanosheets

Owing to their tunable direct bandgap, high charge carrier mobility, and unique in-plane anisotropic structure, black phosphorus nanosheets (BPNSs) have emerged as one of the most important candidates among the 2D materials beyond graphene. However, the poor ambient stability of black phosphorus limits its practical application, due to the chemical degradation of phosphorus atoms to phosphorus oxides in the presence of oxygen and/or water. Chemical functionalization is demonstrated as an efficient approach to enhance the ambient stability of BPNSs. Herein, various covalent strategies including radical addition, nitrene addition, nucleophilic substitution, and metal coordination are summarized. In addition, efficient noncovalent functionalization methods such as van der Waals interactions, electrostatic interactions, and cation-π interactions are described in detail. Furthermore, the preparations, characterization, and diverse applications of functionalized BPNSs in various fields are recapped. The challenges faced and future directions for the chemical functionalization of BPNSs are also highlighted.