# Noble Metal-Based Heterogeneous Catalysts for Electrochemical Hydrogen Evolution Reaction
## 4 Noble Metal-Based Heterogeneous Catalysts
### Interface Engineering
#### 4.2.2 D Structure Hybrid Nanostructures Loaded with Noble Metals
They are a large class of 2D transition metal carbides/nitrides derived from the selectively etched layered MAX phase [111]. MXene can generally be expressed as M\({}_{\text{n+1}}\)X\({}_{\text{n}}\)T\({}_{\text{x}}\) (\(n\) = 1-3), where M is the transition metal (e.g., Ti, Mo, Nb, Ta or V), X is the C and/or N elements and T represents the surface groups, such as -OH, -O, and -F [112]. MXene has abundant surface chemical properties, high hydrophilicity, mechanical stability, metal conductivity related to high electron density near the Fermi level and other favorable properties [113; 114]. For example, [PERSON] et al. [86] mixed a H\({}_{2}\)PtCl\({}_{6}\) solution with an MXene solution to form MXene@Pt, and adopted single-walled carbon nanotubes (SWCNTs) as a binder and fluid collector to obtain a layered Pt-MXene-CNT heterostructure. The overpotential is 62 mV at 10 mA cm\({}^{-2}\) in 0.5 M H\({}_{2}\)SO\({}_{4}\), and the Tafel slope is 66.6 mV dec\({}^{-1}\). The abundant negatively charged groups on the surface of MXene are conducive to the adsorption of noble metal cations and stabilize the reduced noble metal nanoparticles, effectively preventing their aggregation. * LDHs, Layered Double Hydrooxides The general formula of LDHs is [M\({}_{\text{1-x}^{2+}}\)M\({}_{\text{x}}\)\({}^{3+}\)(OH)\({}_{2}\)]A\({}_{\text{x}}\)/n\({}^{\text{n-}}\)\(\cdot\)mH\({}_{2}\)O, which is composed of a positively charged brucite layered body and exchangeable charge-balanced interlayer anions. A divalent metal ion (e.g., Mg\({}^{2+}\), Fe\({}^{2+}\), Co\({}^{2+}\), Cu\({}^{2+}\), Ni\({}^{2+}\) or Zn\({}^{2+}\)) is partially coordinated by a hydroxyl octahedron, which can be replaced by a trivalent metal ion (e.g., Al\({}^{3+}\), Cr\({}^{3+}\), Ga\({}^{3+}\) or Mn\({}^{3+}\)) in a brucite layer. One example of the charge-balanced anion is CO\({}_{3}\)\({}^{2-}\). mH\({}_{2}\)O represents the interlayer water molecules [115]. LDHs have attracted extensive attention in the field of electrocatalysis due to their adjustability of metal cations, interlayer anion exchangeability and easy stripping into monolayer nanosheets. However, their poor electrical conductivity restrict their large-scale applications [46]. Researchers have tried to solve this problem by mixing LDH with conductive materials, growing LDH directly on conductive materials (carbon nanotubes, graphene, etc.) or electrode substrates such as nickel foam and carbon fiber cloth [102; 116]. For example, [PERSON] et al. [95] grew NiFe LDH in situ on carbon cloth (CC) decorated with ultrafine Pt sub-nanoclusters (average size of 0.59 nm). Highly evenly dispersed Pt can expose more active sites, shorten the  
Figure 9: (**a**) HRTEM image of PtRu NCs/BP (Insert: Lattice fringes of the single NC in the yellow frame). (**b**) Current densities of Pt NCs, PtRu NCs, Pt/C, PtRu NCs/BP and Pt NCs/BP at an overpotential of \(-\)70 mV. (**c**) Reaction energy diagram of water dissociation on freestanding and BP supported Pt\({}_{\text{55}}\) and Pt\({}_{\text{22}}\)Ru\({}_{\text{33}}\)NCs. (**d**) Free energy diagrams for hydrogen evolution at zero potential on the freestanding and BP supported NCs, as well as the bare oxidized BP monolayer [94]. Copyright 2019 American Chemical Society. electron transport path and considerably reduce the amount of Pt. In addition, the strong interaction between Pt and 2D NiFe LDH can effectively prevent the aggregation of Pt sub-nanoclusters. * MOFs, Metal-Organic Frameworks  
Metal-organic framework (MOF) materials consisting of central metals, and organic ligands are receiving increasing attention. In particular, 2D MOF nanosheets have become one of the most popular materials in current research, due to their large specific surface area, high proportion of exposed metal atoms, porous structure and adjustable surface functional groups [117]. By introducing additional substrate to construct 2D MOF-based nanocomposites, its intrinsic catalytic activity can be further improved and the feasibility of material application can be expanded [118].