Atomically miniaturized bi-phase IrOx/Ir catalysts loaded on N-doped carbon nanotubes for high-performance Li–CO2 batteries

Abstract

Li–CO₂ batteries are bifunctional, spontaneously storing energy and fixing environmental CO₂ without external electricity. Identifying efficient catalysts that can accelerate the reversible formation and decomposition of the insulating carbonate products formed on the electrode remains challenging. To overcome this limitation, we atomically dispersed IrO_x/Ir bi-phase particles as single-atom catalysts (SACs) on nitrogen-doped carbon nanotubes (NCNTs) and introduced them to facilitate a reversible Li–CO₂ reaction with low overpotential and stable cycle performance for 120 cycles. The IrO_x/Ir SACs were successfully minimized to an atomic scale of 4 Å and formed unique surface oxides via dangling bonds on the atomic Ir catalyst, enhancing the surface catalytic activities. The N sites doped on the carbon nanotubes increased the electronic conductivity and provided favorable nucleation sites for Ir loading. The Li–CO₂ cells employing IrO_x/Ir SACs loaded on NCNTs exhibited improved cell performance, reduced polarization, lower charge transfer resistance, and higher stable cyclability compared to cells employing larger-sized Ir particles on NCNTs. The reversible Li–CO₂ reaction mechanism facilitated by the IrO_x/Ir SAC-loaded NCNT catalyst is explained through density functional theory (DFT) calculations that demonstrated that the bond of SACs with (Li⁺ + e⁻) is strong and forms products, whereas the bond with is weak and evolves products reversibly. This strategy to atomically minimize noble metal catalysts may facilitate the realization of high-performance and economical Li–CO₂ batteries to achieve carbon-negativity targets.