heets are prepared from the in situ topotactic transformation of bismuth oxyiodide nanosheets. They process single crystallinity and enlarged surface areas. Such an advantageous nanostructure affords the material with excellent electrocatalytic performance for carbon dioxide reduction to formate. High selectivity (~100%) and large current density are measured over a broad potential, as well as excellent durability for >10 h. Its selectivity for formate is also understood by density functional theory calculations. In addition, bismuth nanosheets were coupled with an iridium-based oxygen evolution electrocatalyst to achieve efficient full-cell electrolysis. When powered by two AA-size alkaline batteries, the full cell exhibits impressive Faradaic efficiency and electricity-to-formate conversion efficiency.23:T4bc,The electrocatalytic reduction reaction of CO₂ (CO₂RR) is a promising strategy to promote the global carbon balance and combat global climate change. Herein, exclusive Bi-N₄ sites on porous carbon networks can be achieved through thermal decomposition of a bismuth-based metal-organic framework (Bi-MOF) and dicyandiamide (DCD) for CO₂RR. Interestingly, in situ environmental transmission electron microscopy (ETEM) analysis not only directly shows the reduction from Bi-MOF into Bi nanoparticles (NPs) but also exhibits subsequent atomization of Bi NPs assisted by the NH₃ released from the decomposition of DCD. Our catalyst exhibits high intrinsic CO₂ reduction activity for CO conversion, with a high Faradaic efficiency (FE_CO up to 97%) and high turnover frequency of 5535 h^-1 at a low overpotential of 0.39 V versus reversible hydrogen electrode. Further experiments and density functional theory results demonstrate that the single-atom Bi-N₄ site is the dominating active center simultaneously for CO₂ activation and the rapid formation of key intermediate COOH* with a low free energy barrier.

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