Tin Nanoparticles Unblock the Potential of Iron-Chromium Flow Batteries

Renewable energy relies on effective storage to smooth out intermittent supply, and iron-chromium flow batteries (ICFBs) have long been considered a strong candidate for the electrical grid. However, their practical deployment has been hampered by two fundamental issues: sluggish redox kinetics—meaning the chemical reactions happen too slowly—and the unwanted generation of hydrogen gas, known as the hydrogen evolution reaction (HER), which wastes energy and reduces efficiency.

To resolve these bottlenecks, researchers introduced a scalable method to uniformly coat graphite felt with tin (Sn) nanoparticles. This modification serves a dual purpose. Firstly, the tin acts as a potent catalyst. Detailed analysis reveals that the nanoparticles mediate ‘chloride-bridging interactions’, which help in stabilising reaction intermediates and lowering the energy barriers for electron transfer. This significantly speeds up the critical chromium reaction kinetics required for the battery to function effectively.

Secondly, the tin coating suppresses the troublesome hydrogen production. It increases the energy required for hydrogen to bind to the electrode surface, effectively reducing its ability to form. By spatially separating the chromium reaction sites from proton-rich zones, the design ensures electrons are used for storage rather than gas generation. The results are impressive: an ICFB using this Sn-modified felt achieved an energy efficiency of over 79% and a coulombic efficiency exceeding 98%. Moreover, an 1800 W battery stack demonstrated stable performance over 100 cycles, underscoring the strategy's potential for real-world application.