ИСТИНА

Nowadays essential needs in the energy storage for high power applications predetermine designing of the new efficient power sources. Oxygen reduction and evolution reaction (ORR and OER) underlies the most perspective electrochemical current sources e.g. lithium-air (or Li-oxygen) batteries (LAB) and fuel cells. The LAB has high specific energy and huge capacity overcoming such of lithium-ion batteries by five times of magnitude [1]. Carbon materials are ideally suited for positive electrode due to their low cost and low specific weight. Unfortunately, the sustainable operation of LABs with carbon cathodes is not demonstrated yet and the cycleability is quite poor. Recently we successfully implemented photoemission spectroscopy of lithium-oxygen electrochemical cell at true operando conditions at the ISISS beamline (BESSY II) [2]. By introducing oxygen pressure in analysis chamber up to 0.3 mbar, we observed highly reactive superoxide radicals are being formed during discharge of the specially designed electrochemical cell lithium-oxygen cell. Superoxide radicals interact with carbon material resulting in Li2CO3 formation and thus degradation of carbon electrode [2]. This experiment allowed us to suggest the underlying mechanism for both discharge and recharge processes occurring at the carbon electrode surface and reveal conditions for carbonate formation resulting to electrode degradation. Besides, we found the essential difference in this process between more defect reduce graphite oxide (RGO) and much less defect thermal expanded graphite (TEG). We also studied electrode materials alternative to carbons like carbides and nitrides. For instance, for TiC better stability was reported [3]. However, the question how electrode material is included in the electrochemical process and which material property is responsible for this is fully enigma. Operando studies of the chemical changes occurring at the carbide positive electrodes helped us to reveal individual reaction steps and mechanisms of LAB cycling. Thus, near ambient pressure XPS presents unique instrument to probe the surface chemistry of the discharge and recharge processes in Li-air batteries and facilitate the understanding of how the electronic properties and structure of the electrode materials determine their electrocatalytical properties. This, in turn, will support the search of proper electrode materials