Highly porous N-doped activated carbon monoliths (ACMs) are fabricated by carbonization and physical activation of mesoporous polyacrylonitrile (PAN) monoliths in the presence of CO(2). The monoliths exhibit exceptionally high CO(2) uptake; 5.14 mmol g(-1) at ambient pressure and temperature and 11.51 mmol g(-1) at ambient pressure and 273 K.

In lithium oxygen (Li–O2) batteries, controlling the structure of lithium peroxide (Li2O2) can reduce the large overpotential of the charge process as this affects the ionic and electronic conductivities of Li2O2. We demonstrate, for the first time, the in situ structural tuning of Li2O2 during the discharge process by virtue of the surface properties of carbon nanotube electrodes. We tailored carbon nanotube surfaces to decouple oxygen functional groups, defective edges, and graphitization, which directly influence the surface-binding affinity of O2 and LiO2. Consequently, conformal and completely amorphous Li2O2 films form in the presence of oxygen functional groups, which can facilely decompose in the subsequent charge. In contrast, crystalline Li2O2 particles grow in more ordered carbon electrodes and consequently require higher overpotential for decomposition. Our comprehensive study reveals the possibility of facile decomposition of Li2O2 by the surface engineering of carbon electrode and gives insights into the parameters to improve Li–O2 cell performance without any additional promoters such as nanoparticles or soluble redox mediators. In all, this work provides improved understanding of the general role of carbonaceous electrode surfaces toward the enhancement of discharge capacity, charge potential, and stability.

In lithium−oxygen (Li−O 2 ) batteries, nanocatalysts have been widely employed as a means to suppress the large recharge overpotential and to possibly improve cyclability. However, these studies have consistently been mired with ambiguity relating to the possible exacerbation of side reactions, which in turn has brought into question the role of such catalysts in Li−O 2 cells. Here, we shed light on the viability of nanocatalysts by examining the use of Ru, Pt, Pd, Co 3 O 4 , and Au nanoparticles supported on carbon nanotubes in Li−O 2 cells. We show that while there can be noticeable reduction in overpotential with catalysts, the facile decomposition of Li 2 O 2 is not accompanied by a decrease in side reactions, and as a consequence, there is no notable improvement in rechargeability or cyclability. Instead, highly active catalysts can exhibit nonselectivity for all oxidation reactions including Li 2 O 2 and the electrolyte. This work underscores the importance of metrics beyond simple consideration of the recharge overpotential and the necessity of pursuing approaches that can promote reversible Li−O 2 electrochemistry.