Deciphering Electrocatalytic Sulfur Reduction Reactions in Al–S Batteries via Single-Particle Electrodes

The kinetically sluggish sulfur reduction reaction (SRR) governs the performance of ultrahigh-capacity aluminum–sulfur batteries, while deciphering the SRR process is critical for rationally electrocatalyzing reaction kinetics to unlock their full energy output. To overcome this challenge, a single-particle electrochemical methodology has been developed to investigate the SRR process on a cobalt/nickel and nitrogen codoped graphene (CoNi-NG) electrocatalyst. The SRR process involves a major route of S8 → Al2S8 → Al2S4 → Al2S3 with a minor route of Al2S8 → Al2S6 → Al2S4, where Al2S4 conversion governs the overall SRR kinetics and Al2S4 contributes the most to the shuttle effect owing to its fastest generation and slowest consumption. The CoNi-NG raises the Co d-orbital energy level via Ni-to-Co electron transfer to accelerate cleavage of polysulfides, which doubles the exchange current density of rate-determining Al2S4 conversion. Consequently, the sulfur composite (S@CoNi-NG) electrode delivers a specific capacity of ∼1480 mAh gsulfur–1. Such a single-particle methodology for quantitatively deciphering electrocatalytic SRRs offers mechanistic guidance for rationally enhancing battery performance.