Increasing electron transfer and light absorption in graphited nanocarbon-conjugated g-C3N4 nanosheet heterostructure for photocatalytic hydrogen evolution

Accelerating the charge separation and transfer as well as increasing the visible light absorption is of great importance for photocatalysts to realize efficient photocatalytic hydrogen evolution via water splitting. Herein, for the first time, we fabricated in-plane graphited nanocarbon-conjugated polymeric carbon nitride (GNC-C₃N₄) nanosheet heterostructure photocatalyst from melamine and hexaketocyclohexane octahydrate mixture via an amino-carbonyl reaction. The incorporation of GNC into conjugate network of C₃N₄ can not only dramatically enhance the light harvesting but also significantly promote the charge separation and transfer by the built-in electric field and intimate interface in the coplanar GNC-C₃N₄ heterostructure. Accordingly, the optimal GNC-C₃N₄ photocatalyst demonstrates a more than 15-fold enhancement for photocatalytic hydrogen evolution from water under visible light irradiation, compared to C₃N₄.     

Synthesis of Fe3O4 nanocubes anchored in MgCo2O4 nanoneedle arrays for flexible all-solid-state asymmetric supercapacitor

The design of novel heterostructure with multifunctional characteristics is of great technical significance for the development of new energy storage devices. However, the lower conductivity of metal oxides and the accumulation caused by irreversible phase transition after multiple cycles are the main reasons for the low specific capacitance and cycle life. Herein, we synthesized bimetallic oxide MgCo₂O₄ nanoneedles with a spinel structure, and firmly anchored Fe₃O₄ nanocubes on MgCo₂O₄ nanoneedles by ion-exchange strategy. Thanks to the constructed heterostructure of nanoneedles/nanocubes, the introduction of Fe₃O₄ effectively improves the electron transport path in MgCo₂O₄ during repeated charging and discharging, and increases the effective activation sites involved in electron transfer. As a result, a higher specific capacitance of 1648 F g^?1 at 1 A g^?1 and an ultra-long cycle life of 78.6% capacitance retention after 6000 continuous charge/discharge cycles are obtained. A flexible all-solid-state asymmetric supercapcitor assembled with MgCo₂O₄-Fe₃O₄ as positive electrode and AC as negative electrode can deliver an ultra-high energy density of 78 Wh kg^?1 and maximum power density of 1.2 kW kg^?1, as well as extraordinary capacitive retention of 75.2% after 10,000 cycles. These excellent properties reveal the potential and application value of MgCo₂O₄-Fe₃O₄ in the development of high-performance supercapacitors.     

Construction of heterostructured g-C3N4@TiATA/Pt composites for efficacious photocatalytic hydrogen evolution

Construction of heterostructured photocatalysts is a feasible method for improving hydrogen production from water splitting because of its good charge transport efficiency. Herein, we coupled the Ti-MOFs (TiATA) with metal-free graphitic carbon nitride (g-C₃N₄) to synthesize composites, g-C₃N₄@TiATA, in which a heterostructure was formed between g-C₃N₄ and TiATA. The establishment of heterojunctions not only broadens the light absorption range of g-C₃N₄@TiATA (490 nm) by contrast with g-C₃N₄ (456 nm), but also greatly accelerates charge migration. Photocatalytic studies present that the construction of heterostructure steering the charges flow from g-C₃N₄ to TiATA and then delivery to the cocatalyst of Pt nanoparticles, exhibiting an impressively photocatalytic hydrogen production rate (265.8 μmol·h⁻¹) in assistance of 300 W Xenon lamp, which is about 3.4 times as much as g-C₃N₄/Pt.     

Construction of 1D/0D/2D Zn0.5Cd0.5S/PdAg/g-C3N4 ternary heterojunction composites for efficient photocatalytic hydrogen evolution

A high-efficiency and easy-available approach was developed to obtain a ternary heterojunction composites with advanced hydrogen evolution reaction (HER) performance under visible light by water split. PdAg bimetallic nanoparticles make a close contact interface between g-C₃N₄(CN) and Zn_0.5Cd_0.5S(ZCS). Under visible light irradiation, CN and ZCS are both excited to generate electron-hole pairs, PdAg bimetallic nanoparticles act as a bridge between CN and ZCS. Not only can the photogenerated electrons from CN be captured, but they can also be quickly transferred to the surface of ZCS and participate in the photocatalytic reaction to release H₂, and the recombination of charge carriers between the contact interface of ZCS and CN can be significantly inhibited. In addition, the thin CN layer reduces the photocorrosion of the ZCS and enhances the specific surface area of the composite material. After testing, the composite material with 30 wt% ZCS and 4 wt% PdAg demonstrates hydrogen evolution performance, up to 6250.7 μmol g^?1h^?1, which is 753 times the hydrogen evolution rate of single-component CN and 12.6 times of ZCS/CN. Compared with single-component and two-component photocatalysts, the ternary ZCS/PdAg/CN photocatalyst achieves significantly enhanced photocatalytic activity.     

Phosphatizing engineering of heterostructured Rh2P/Rh nanoparticles on doped graphene for efficient hydrogen evolution in alkaline and acidic media

A wide diversity of phosphides of platinum-group metal including Rh, Ru and Ir exhibit intriguing electrocatalytic activity toward hydrogen evolution reaction (HER). The phosphidation degree, namely the P dosage in these phosphides shows pronounced influence on the catalytic performance but is hard to control. In this work we developed a reliable strategy to synthesize Rh₂P-based nanoparticles with controlled phosphidation degree, and investigated the influence of phosphidation degree on HER. It is found that the heterostructured Rh₂P/Rh nanoparticle, i.e., the P-deficient composite with mixed metallic and phosphide phases, outperforms either the metallic Rh or pure Rh₂P nanoparticles. As-synthesized Rh₂P/Rh nanoparticles supported on P/N co-doped graphene (denoted as Rh₂P/Rh-G) display remarkable HER activity with tiny overpotential of 17 and 19 mV at 10 mA cm^?2 current density in alkaline and acid, efficiently surpassing its Rh-based rivals and benchmark Pt/C catalyst. Meanwhile it illustrates a large mass-specific activity (3.23 and 6.26 A mg^?1 @50 mV overpotential in alkaline and acid, respectively) due to its high activity and low metal loading. Density functional theory (DFT) calculation indicates that the Rh₂P/Rh heterostructured interface possesses the optimal close-to-zero value of hydrogen adsorption energy and water dissociation process is accelerated, and thus boosts HER activity.     

In-situ facile synthesis of heterostructural Co||MnCo2O4.5/NC with active oxygen vacancies and its bifunctional electrocatalysis for oxygen reduction and oxygen evolution reaction

A potential non-noble metal oxide catalyst with its low-cost and efficient catalytic ability attract increasing attention. In this paper, a highly efficient bifunctional electrocatalyst Co||MnCo₂O_4.5/NC with heterostructure and oxygen vacancies is prepared utilizing solid reaction in-situ. The optimal catalyst is obtained at 650 °C with the mass ratio (1:8) of MnCo₂O_4.5 and Dicyandiamide (DCD). It shows excellent electrocatalytic activity for oxygen reduction reaction (ORR) with high half-wave potential (0.81 V) and limit current density (6.22 mA cm^?2), which is better than that of the commercial 20% Pt/C(0.81 V, 5.52 mA cm^?2). At the same time, it also exhibits superior electrocatalytic activity for oxygen evolution reaction (OER) with low overpotential (330 mV) and a faster dynamics process. The superior electrocatalytic properties may be resulted from the presence of heterostructure and increasing ratio of oxygen vacancies, which helps to the rapid transfer of electrons and creates more active sites. Moreover, the self-generated N-doped carbon provides high conductivity of the as-prepared Co||MnCo₂O_4.5/NC composite. It can be seen that the application of interface engineering technologies is useful for improving the performance of the catalyst, providing an effective and facile synthesis strategy for non-noble metal catalyst.     

Fabrication of robust CoP/Ni2P/CC composite for efficient hydrogen evolution reaction and the reduction of graphene oxide

Developing the novel catalysts with an excellent performance of hydrogen generation is essential to facilitate the application of hydrogen evolution reaction (HER). Herein, a heterostructured cobalt phosphide/nickel phosphide/carbon cloth (CoP/Ni₂P/CC) composite was fabricated via an interfacial engineering strategy to achieve the modification of CoP nanoleaf on Ni₂P nanosheet skeleton supported by carbon cloth. By virtue of the unique heterostructure, abundant exposing active sites and the synergistic coupling effect of CoP and Ni₂P nanoparticles, the elaborated CoP/Ni₂P/CC composite exhibits a robust catalytic property. Among fabricated composites, the optimal CoP/Ni₂P/CC-4 catalyst behaves an excellent HER performance at a wide pH range (overpotentials of 67, 71 and 95 mV to afford 10 mA cm^?2 in 0.5 M H₂SO₄, 1 M KOH and 1 M PBS, respectively). The HER current density of this composite shows a negligible degradation after continuous test for 24 h. Charmingly, the HER process of this catalyst was innovatively applied to reduce graphene oxide, and thus exploiting the fabrication route of reduced graphene oxide (rGO). We are sure that this work will provide a firm guideline for the exploitation of pH-universal HER catalysts and the exploration of HER application.     

Stainless steel mesh-based CoSe/Ni3Se4 heterostructure for efficient electrocatalytic overall water splitting

The construction of high-efficiency bifunctional electrocatalysts is still a main challenge for hydrogen production from water splitting, in which comprehensive structure regulation plays a key role for synergistically boosting the intrinsic activity and charge collection. Here, we used a two-step hydrothermal method for construction of an interjaculated CoSe/Ni₃Se₄ heterostructure from NiCo LDH nanosheets grown on stainless steel (SS) meshes as bifunctional electrocatalysts for overall water splitting. The SS meshes containing Fe and Ni act as an excellent 3D scaffold for catalyst growth and charge collection. The SS@CoSe/Ni₃Se₄ composite exhibits outstanding electrocatalytic performances with low overpotentials of 97 mV for hydrogen evolution and 230 mV for oxygen evolution to reach a current density of 10 mA cm⁻², respectively. Moreover, by using SS@CoSe/Ni₃Se₄ as both the cathode and anode, the assembled electrolyze only required 1.55 V to reach 10 mA cm⁻² for overall water splitting. The outstanding performance of SS@CoSe/Ni₃Se₄ benefits from the synergy between excellent charge collection capability of SS meshes and the abundant active sites at the CoSe/Ni₃Se₄ heterointerface formed with the in-situ conversion of NiCo LDH nanosheets. Electrochemical active surface area and impedance spectrum indicate that the CoSe/Ni₃Se₄ loaded on SS has the most abundant electrochemically active sites and the smallest electrochemical resistance, thereby exposing more active sites and enhancing the charge transfer to promote the catalytic activity. By integrating the delicate nanoscale heterostructure engineering with the microscale SS mesh scaffold, our work provides a new perspective for the preparation of high-performance and cheap electrocatalysts that are easy to be integrated with industrial applications.     

Fe7Se8@Fe2O3 heterostructure nanosheets as bifunctional electrocatalyst for urea electrolysis

Water electrolysis for producing hydrogen is considered to be the most feasible means to develop new green energy. Compared with above, urea electrolysis can improve energy conversion efficiency by introducing urea, and can also be used for purification of wastewater rich in urea. In this paper, a bifunctional electrocatalyst with heterostructure, namely Fe₇Se₈@Fe₂O₃ nanosheets supported on nickel foam, were synthesized for the first time through typical hydrothermal and partial oxidation processes. Iron cation promotes electron transfer and adjusts electron structure under the synergistic action of selenium and oxygen anion, thus achieving excellent catalytic activity of urea electrolysis. In an alkaline solution of 1 M KOH with 0.5 M urea, the Fe₇Se₈@Fe₂O₃/NF catalyst can drive the current density of 10 mA cm^?2 with requiring only potential of 1.313 V and overpotential of 141 mV for urea oxidation reaction (UOR) and hydrogen evolution reaction (HER), respectively. What is noteworthy is that Fe₇Se₈@Fe₂O₃/NF heterostructure is used as bifunctional electrocatalyst to form urea electrolyzer device, which only needs potential of 1.55 V to drive current density of 10 mA cm^?2, which is one of the best catalytic activities reported so far, and the electrode couple showed remarkable stability for 15 h. Density functional theory shows that the Fe₇Se₈@Fe₂O₃/NF material exhibits the minimum Gibbs free energy for the adsorption of hydrogen. This work provides a new method for exploring novel and environmentally friendly bifunctional electrocatalysts for urea electrolysis.     

Influence of van der waals heterostructures of 2D materials on catalytic performance of ZnO and its applications in energy: A review

Recently, photocatalysis has received huge attention in order to overcome energy crisis worldwide. Many semiconductors, potential schemes and hierarchies have come to light during past few decades to fabricate efficient catalysts however, among all these methods heterostructures have taken the world by surprise. With the advancement in post-graphene 2D materials, van der Waals heterostructures have come to light exploring enhancement in photocatalysis. During a very short period a number of ZnO-based van der Waal heterostructures have taken the limelight in the field of photocatalysis. First principles calculations and DFT approach towards the heterostructures of GeC, GaN, WSe₂, WS₂ and other layered 2D materials unleased a series of properties and facts for the provision of enhanced catalysis. Reduction in bandgap of ZnO has also been observed which widens the pathways towards visible light irradiation. However, energy applications of zinc oxide are also fascinating feature as it can serve as a photoanode to replace TiO₂. Whereas the famous hydrogen production, batteries and solar cells have also been fabricated by the use of this semiconductor.