Two-dimensional materials have attracted broad interest because of their wide variety of properties. They can be used as photocatalysts and electrocatalysts due to their extremely high specific surface area, and have great potential application in the field of environment and renewable energy. This review focuses on the structure and properties of common two-dimensional materials such as 2D carbides and nitrides (MXenes), g-C₃N₄ and black phosphorus (BP). Furthermore, the latest research on the modification of two-dimensional materials in the area of photocatalysis and electrocatalysis are discussed and commented. Finally, research prospects for two-dimensional materials in the future are predicted.

Highly efficient TiO₂ photocatalysts (TiO₂/Ag-Ag₂O) co-modified by Ag as electron cocatalysts and Ag₂O as interfacial catalytic active sites were synthesized via a two-step process including the initial photoinduced deposition of metallic Ag nanoparticles on the TiO₂ surface (TiO₂/Ag) and the following in situ oxidation of partial Ag into Ag₂O by low-temperature calcination. Ag nanoparticles function as effective electron cocatalysts for the steady capture and rapid transportation of photogenerated electrons from TiO₂ surface to Ag₂O, while the adsorbed H⁺ ions from solution to Ag₂O as the interfacial catalytic active sites are reduced into H₂. The synergistic effect of Ag and Ag₂O can accelerate the electrons transfer and promote the rapid H₂-evolution reaction for enhanced photocatalytic H₂-evolution performance of TiO₂/Ag-Ag₂O. The highest H₂-evolution rate of the resultant TiO₂/Ag-Ag₂O calcinated at 300 ℃ reached 75.20 μmol/h, which was higher than those of the TiO₂ (3.59 μmol/h) and TiO₂/Ag (41.13 μmol/h) by 21.0 and 1.8 times, respectively. This study provides a new strategy for the design and synthesis of highly efficient photocatalytic H₂-evolution materials.

Herein, we report a kind of NiCu-based composite phosphides electrocatalyst(NiCuP/NM), which was prepared in situ on nickel mesh substrate by one-step hydrothermal method with NaH₂PO₂, CuSO₄, NiSO₄ as initial materials. The morphology, crystal structure, composition, and electrocatalytic performance of NiCuP/NM were characterized. Under the optimal preparation conditions of Ni, Cu and P(molar ratio 8 : 1 : 20), hydrothermal synthesis at 140 ℃ for 24 h, the obtained composite electrocatalyst displayed three-level micro-nanostructure with Ni₂P and Cu₃P as main crystal phases. At the current density of 10 mA·cm ^-2, the required HER (Hydrogen Evolution Reaction) overpotential and HzOR (Hydrazine Oxidation Reaction) potential of NiCuP/NM were 165 and 49 mV, respectively. In the two-electrode system, the decomposition tank pressure for the NiCuP/NM cell at the same current density was only 0.750 V which remained substantially unchanged for 24 h catalysis, exhibiting excellent catalytic stability. NiCuP/NM displays prominent electrocatalytic performances towards HER or HzOR in both three-electrode and two-electrode systems, which can be ascribed to two aspects. On the one hand, the 14-fold electrochemical active surface area compared with original nickel mesh enables NiCuP/NM expose huge number of catalytic active sites in both HER and HzOR. On the other hand, the electronic structure modification of Ni and Cu atoms induced by doping P atom brings great improvement of intrinsic HzOR activity of electrode materials. This study provides a new perspective for nanoscale synthesis and promotes the development of novel nanopores in fuel cell and energy conversion applications.

The mechanism of Fe-N/C catalysts in oxygen reduction reactions is critical to the development of efficient, sustainable non-noble metal catalysts in polymer electrolyte membrane fuel cells, but it is still in controversy. In order to understand the relationship between composition and the nanostructure of material and the electrochemical activity, this study developed a type of Fe-N/C catalyst with high electrochemical activity, which contained Fe-N_x active sites and Fe/Fe₃C nanocrystals encapsulated with nitrogen-doped carbon nanotubes. Despite being free of precious metals, the as-prepared catalyst displays high oxygen reduction reactions (ORR) activity in alkaline medium with the half-wave potential of 0.86 V(vs RHE), the mass activity of 18.84 A/g at 0.77 V(vs RHE), and the maximum current density of -4.3 mA·cm ^-2. Meanwhile, the electron transfer number is 3.7 at 0.2 V(vs RHE), revealing that the 4-electron ORR reaction exists in the catalyst. The excellent electrochemical activity is attributed to the graphene-encapsulated metallic Fe/Fe₃C nanocrystals which improves the conductivity after the growth of N-doped carbon nanotubes, and the relatively high proportion of Fe-N_x active sites distributed on the surface of Fe/Fe₃C nanoparticles. This study provides a certain reference and basis for the further study of non-noble metal catalyst and their wide application in commercial production.

BiVO₄ film was synthesized via template method, the ferroelectric material BiFeO₃ was prepared by Sol-Gel method to modify BiVO₄. By means of dual-ferroelectric semiconductor composition, the photochemical properties of BiVO₄ was greatly improved. The electrochemical test results show that the superior photoelectrochemical properties of BiVO₄ film are achieved after spin-coating with BiFeO₃ for 5 times. It owns an optimal photocurrent density of 0.72 mA·cm^-2, which is 67.4% higher than that of pure BiVO₄. The energy band bending regulation via electric field polarization could further boost the photoelectrochemical property of BiVO₄/nBiFeO₃ ferroelectric composite. The highest photocurrent density of the composite after polarization at 20 V reaches 0.91 mA·cm^-2, which is more than twice of pure BiVO₄ film. The combination of BiFeO₃ and BiVO₄ is favorable for forming heterojuncting, generating and separating of photogenic electrons and holes. The electric field polarization regulating band bending accelerates the photogenic charge transfer, which is the main reason for the improved photoelectrochemical properties of ferroelectric composite.

In order to study the influence mechanism of heat treatment and heterostructures on the photoelectrochemical effect of WO₃, monoclinic WO₃ nanoflowers were synthesized by low-temperature solvothermal method. The active crystal fact, grain size and crystallinity of WO₃ were controlled by heat treatment. Furthermore, WO₃/CdS/α-S heterojunction was obtained by modified chemical bath deposition, and the concentration effect of its photoelectrochemical performance was studied. The results show that the (200) crystal plane with photoelectrochemical activity is the main exposed crystal plane of WO₃, and the proportion of the exposed crystal plane increases with the heat treatment temperature increasing. The WO₃ nanoflower treated at 350 ℃ showed the highest photoresponse current. By constructing WO₃/CdS/α-S heterojunction, the material's absorption in the visible light region is enhanced, and the overall efficiency of photo-generated carrier separation is improved by sacrificing a small amount of carriers, which promotes the macroelectronic chemical effects of WO₃.

Developing highly efficient and low-cost catalysts is crucial in the field of clean energy economy, in which ammonia borane (AB) has attracted great attention due to its high hydrogen production through the catalytic hydrolysis. In this work, BiVO₄ nanosheet was firstly synthesized by a facile reflux method. And then bimetallic RuFe@BiVO₄ catalysts with different molar ratios of Ru/Fe were prepared via in situ impregnation-reduction techniques and their catalytic activities were also tested in the hydrogen generation from aqueous solution of AB at room temperature. Compared with the releasing hydrogen rates of catalysts of BiVO₄, Ru@BiVO₄, Fe@BiVO₄, RuFe NPs and RuFe@BiVO₄, respectively, Ru₁Fe_0.1@BiVO₄ exhibits the highest catalytic activity for the dehydrogenation of AB among all catalysts, the activation energy (E_a) and turnover frequency (TOF) are 43.7 kJ·mol^-1 and 205.4 mol_H2·mol_Ru·min^-1, respectively. The addition of non-noble Fe can significantly enhance the catalytic activity of Ru counterparts, which is closely related to the strong electronic effect between Ru and Fe NPs, bi-functional effect generated between the RuFe NPs and the support BiVO₄.