The performance and detailed flow structure of a counter-rotating compressor under different rotating speed and typical working condition were experimentally and numerically investigated. Numerical results preliminarily showed that the total pressure ratio performance agreed well with experimental data, when the calculated peak efficiency was a little bigger than the experimental one. With optimized speed ratio, the peak isentropic efficiency can be increased with minor reduction of the total pressure ratio and safe margin. Flow reversal fist occurred at the start section of the outlet guide vane and it covered nearly 40 per cent area of the whole flow at the stall point when the rotational speed ratio of rotor 1 and rotor 2 were greater than or equal to 1, and it caused the compressor operate in the stall point. First, however, the flow separation and great range low-energy flow occurred at the 30 per cent span range of s rotor blade-tip near stall point, which was the main reason for the compressor stall when the speed ratio is less than 1. Rotor 2 worked at a greater incidence angle because of the separation at the trailing edge of rotor 1.

Two-dimensional (2D) materials with outstanding electronic transport properties are rigid against bending because of strong in-plane covalent bonding and intrinsically flexible because of the lack of out-of-plane constraint and thus are considered to be promising for flexible thermoelectrics (TEs). As a typical 2D material, MXene, however, exhibited a restricted TE performance because the termination groups and guest molecules in MXene nanosheets introduced by acid etching and reassembly deteriorate intra/interflake conduction. This work realized increases in both the carrier concentration and intra/interflake mobility by the construction of a MXene nanosheet/organic superlattice (SL) and composition engineering, attributed to electron injection, intercoupling strengthening, and defect reduction at the nanosheet edges. An electrical conductivity increased by 5 times, to 2.7 × 105 S m–1, led to power factors of up to ∼33 μW m–1 K–2, which is above the state-of-the-art for similar materials, almost by a factor of 10. A TE module comprising four SL film legs could yield 58.6 nW power at a temperature gradient of 50 K. Additionally, both the annealed film and the corresponding module exhibited excellent reproducibility and stability. Our results provide a strategy to tailor the TE performance of 2D-material films through SL construction and composition engineering.

Construction of an inorganic/organic superlattice-based film has been proven effective in enhancing thermoelectric (TE) performance as well as flexibility by a variety of mechanisms, typically for two-dimensional (2D) TiS2-based flexible TEs. MXenes, typically, Ti3C2T x , are a type of 2D material widely investigated in fields of flexible batteries and electromagnetic shielding, among others. However, they have rarely been reported in flexible TEs. One of the key factors is that the surface termination groups (−T) on an MXene could trap electrons, restricting the electronic transport. Herein, −T groups were tailored and substituted by organic ions (−HA) by facile preannealing, exfoliation, and reassembly. The intercalation of −HA introduced Ti–N bonding, forming a flexible MXene/organic superlattice film. The electrical conductivity of the superlattice film was increased by 5 times to 1.6 × 105 S m–1 due to defect reduction as well as the electron injection effect. While the Seebeck coefficient was maintained, the power factor was increased from 4 to 18 μW m–1 K–2. The TE module based on the superlattice film revealed an output power of 7.6 nW at a temperature gap of 50 K. This work opens up an avenue of fabricating flexible MXene-based TE films by tailoring the surface termination group and constructing inorganic/organic superlattice structures.