Functionalized metallic 2D transition metal dichalcogenide-based solid-state electrolyte for flexible all-solid-state supercapacitors

Highly efficient and durable flexible solid-state supercapacitors (FSSSCs) are emerging as low-cost devices for portable and wearable electronics due to the elimination of leakage of toxic/corrosive liquid electrolytes and their capability to withstand elevated mechanical stresses. Nevertheless, the spread of FSSSCs requires the development of durable and highly conductive solid-state electrolytes, whose electrochemical characteristics must be competitive with those of traditional liquid electrolytes. Here, we propose an innovative composite solid-state electrolyte prepared by incorporating metallic two-dimensional group-5 transition metal dichalcogenides, namely, liquid-phase exfoliated functionalized niobium disulfide (f-NbS2) nanoflakes, into a sulfonated poly(ether ether ketone) (SPEEK) polymeric matrix. The terminal sulfonate groups in f-NbS2 nanoflakes interact with the sulfonic acid groups of SPEEK by forming a robust hydrogen bonding network. Consequently, the composite solid-state electrolyte is mechanically/dimensionally stable even at a degree of sulfonation of SPEEK as high as 70.2%. At this degree of sulfonation, the mechanical strength is 38.3 MPa, and thanks to an efficient proton transport through the Grotthuss mechanism, the proton conductivity is as high as 94.4 mS cm–1 at room temperature. To elucidate the importance of the interaction between the electrode materials (including active materials and binders) and the solid-state electrolyte, solid-state supercapacitors were produced using SPEEK and poly(vinylidene fluoride) as proton conducting and nonconducting binders, respectively. The use of our solid-state electrolyte in combination with proton-conducting SPEEK binder and carbonaceous electrode materials (mixture of activated carbon, single/few-layer graphene, and carbon black) results in a solid-state supercapacitor with a specific capacitance of 116 F g–1 at 0.02 A g–1, optimal rate capability (76 F g–1 at 10 A g–1), and electrochemical stability during galvanostatic charge/discharge cycling and folding/bending stresses

Graphene vs. carbon black supports for Pt nanoparticles: Towards next-generation cathodes for advanced alkaline electrolyzers

The development of efficient and cost-effective water splitting electrolyzers is a fundamental step to support the achievement of climate neutrality by using renewable energy sources to produce green H2 as a form of clean fuel. In this work, we investigated Pt-based nanostructured cathodes for high-performance alkaline electrolyzers (AELs), showing the beneficial effect of graphene over traditional carbon black as nanocatalysts support. By relying on a water-based, scalable, synthetic method, surface-cleaned Pt nanoparticles were successfully produced and strongly anchored to defect-free graphene flakes, the latter produced through wet-jet milling exfoliation of natural graphite. Once deposited on conventional gas diffusion layers, Pt/graphene catalysts outperform traditional Pt on Vulcan (Pt/C) in terms of hydrogen evolution reaction (HER) activity and performance durability. The two-dimensional morphology of graphene flakes strongly retains the catalysts in the electrode even in the absence of any binder, while intrinsically ensuring the exposure of the catalytic sites for the HER. This rationale enables the fabrication of high-performance AELs based on Pt/graphene cathodes. By using commercially available cost-effective anodes (stainless-steel meshes), our AELs reached current densities of 1 A cm−2 at a voltage of as low as 1.71 V. These AELs can even operate up to more than 2 A cm−2 (e.g., 2.2 A cm−2 at 1.90 V), with stable performance during accelerated stress tests. Our study discloses two main aspects: (1) graphene is an effective conductive support for 1–10 nm-scale catalysts for the development of nanostructured cathodes with elevated catalytic properties and durable performance; (2) the use of efficient nanostructured cathodes can boost the AEL's performance to state-of-the-art values reported for proton-exchange membrane electrolyzers, avoiding the use of expensive anodes (e.g., Ir-based ones)