As one of the most effective synthesis tools, layer-by-layer (LbL) self-assembly technology can provide a strong non-covalent integration and accurate assembly between homo- or hetero-phase compounds or oppositely charged polyelectrolytes, resulting in highly-ordered nanoscale structures or patterns with excellent functionalities and activities. It has been widely used in the developments of novel materials and nanostructures or patterns from nanotechnologies to medical fields. However, the application of LbL self-assembly in the development of highly efficient electrocatalysts, specific functionalized membranes for proton exchange membrane fuel cells (PEMFCs) and electrode materials for supercapacitors is a relatively new phenomenon. In this review, the application of LbL self-assembly in the development and synthesis of key materials of PEMFCs including polyelectrolyte multilayered proton-exchange membranes, methanol-blocking Nafion membranes, highly uniform and efficient Pt-based electrocatalysts, self-assembled polyelectrolyte functionalized carbon nanotubes (CNTs) and graphenes will be reviewed. The application of LbL self-assembly for the development of multilayer nanostructured materials for use in electrochemical supercapacitors will also be reviewed and discussed (250 references).

Controlling multimetallic ensembles at the atomic level is significantly challenging, particularly for high-entropy alloys with more than five elements. Herein, we report an innovative ultrasmall (∼2 nm) PtFeCoNiCuZn high-entropy intermetallic (PFCNCZ-HEI) with a well-ordered structure synthesized by using the space-confined strategy. By exploiting these combined metals, the PFCNCZ-HEI nanoparticles achieve an ultrahigh mass activity of 2.403 A mg_Pt^-1 at 0.90 V vs reversible hydrogen electrode for the oxygen reduction reaction, which is up to 19-fold higher than that of state-of-the-art commercial Pt/C. A proton exchange membrane fuel cell assembled with PFCNCZ-HEI as the cathode (0.03 mg_Pt cm^-2) exhibits a power density of 1.4 W cm^-2 and a high mass-normalized rated power of 45 W mg_Pt^-1. Furthermore, theoretical calculations reveal that the outer electrons of the non-noble-metal atoms on the surface of the PFCNCZ-HEI nanoparticle are modulated to show characteristics of multiple active centers. This work offers a promising catalyst design direction for developing highly ordered HEI nanoparticles for electrocatalysis.

Single-atom catalysts (SACs) of transition metals have attracted enormous attention as replacements of Pt-based catalysts towards the oxygen reduction reaction (ORR). Even though Cu is nature's choice for ORR catalysis in many forms of life from bacteria to humans; however, only a few studies of Cu-based SACs for the ORR have been reported. Furthermore, the applications of Cu SACs for fuel cells have rarely been demonstrated. In this work, we prepared a Cu SAC via a simple pyrolysis method using Cu phthalocyanine as the precursor. The catalyst shows a half-wave potential of 0.81 V (vs. RHE) in alkaline medium towards the ORR, which is 30 mV lower than that of commercial Pt/C (20 wt%). It also shows high durability with only 9 mV negative shift of half-wave potential after 5000 cycles in alkaline medium. An anion exchange membrane fuel cell based on the Cu SAC exhibits a peak power density of 196 mW cm⁻² at 70 °C. The density functional theory calculation suggests that the transformation process from OOH* to O* is the rate determining step over the Cu SAC. The Cu SAC could be a promising non-noble ORR catalyst for fuel cell applications.

Outstanding performance in VRFBs: a novel polysulfone–polyvinylpyrrolidone membrane with high ion selectivity, superior stability and low cost is constructed for VRFBs. The VRFB with the PSF–PVP–50 membrane exhibits impressive CE (98%), EE (89%), and excellent stability during the 2000 h continuous charge–discharge cycling test.