image: A schematic illustrates how FeSn-DSACs use p-d orbital hybridization and a locally negatively charged interface to accelerate ORR while limiting Cl−-induced poisoning of Fe active sites in alkaline seawater.
Credit: ©Science Bulletin
SZABs are attractive for marine energy supply because they are safe, potentially high in energy density and can use abundant seawater as the electrolyte. Yet seawater also brings a problem. At the air cathode, the ORR is slow, and Cl− in seawater can adsorb on Fe active sites, blocking the reaction and accelerating catalyst corrosion.
A research team from Hainan University has now designed FeSn-DSACs to address both issues at once. The work focuses on a simple idea: give Fe, a highly active ORR center, a Sn partner that can reshape its local electronic environment.
In the FeSn-DSACs structure, Fe serves as the main ORR active site, while neighboring Sn regulates the Fe site through p-d orbital hybridization. This Fe-Sn interaction weakens the overly strong adsorption of ORR intermediates on conventional Fe sites and helps create a locally negatively charged interface, making Cl− less likely to poison the Fe active sites.
The researchers first used density functional theory (DFT) calculations to compare several Fe/p-block metal dual-site candidates. FeSn-DSACs showed the best balance between ORR activity and Cl− resistance. They then synthesized the catalyst using a movable-type printing strategy. Microscopy and X-ray spectroscopy confirmed that Fe and Sn were atomically dispersed on nitrogen-doped carbon and stabilized as adjacent dual single-atom sites.
Electrochemical tests in alkaline seawater electrolyte showed that FeSn-DSACs outperformed Fe-SAC, Sn-SAC and commercial 20% Pt/C. The catalyst reached a half-wave potential of 0.900 V versus RHE, followed a near four-electron ORR pathway and showed negligible activity decay after 30,000 accelerated durability test cycles. Post-test XPS showed no observable Fe-Cl signal, supporting the role of FeSn-DSACs in suppressing Cl− adsorption on Fe active sites.
“For seawater batteries, activity alone is not enough,” said Peng Rao, the corresponding author of the study. “The catalyst also needs to drive oxygen conversion efficiently while resisting Cl−-induced poisoning. The Fe-Sn dual-site structure gives us a way to combine these two functions at the atomic level.”
When assembled into flow-type SZABs, FeSn-DSACs demonstrated a peak power density of 255.6 mW cm−2, higher than devices based on Pt/C or Fe-SAC, and operated stably for more than 500 h under the reported testing conditions. The study suggests that p-d orbital engineering can be a useful strategy for designing dual single-atom electrocatalysts for seawater electrochemical systems and other reactions where activity and resistance to Cl− must be improved simultaneously.