A critical assessment of the effect of carbon-based cathode properties on the in situ electrogeneration of H2O2
In the last few years, the in situ H2O2 electrogeneration through the 2e− oxygen reduction reaction (ORR) pathway has increasingly intrigued the scientific community. In particular, a wide experimental campaign has addressed the synthesis of different carbonaceous cathodes. This has resulted in a high number of 2D and 3D cathode materials, either pristine or modified, whose ability to electrogenerate H2O2 in an efficient manner has been tested in different types of electrochemical reactors. Although there is some experimental work correlating the properties of cathode materials with the H2O2 production efficiency, there is no systematic study on this subject. The purpose of this critical review, which is focused on the literature published within the period 2010-2022, is to elucidate the role of the interfacial properties of carbonaceous cathodes in this field. These cathodes can be classified in two categories according to their structure (i.e., crystalline and fibrous), and in five sub-categories: reticulated vitreous carbon (RVC), graphite, carbon felt, graphite felt and gas-diffusion electrode (GDE). These categories are briefly introduced and the performance of materials is compared. Additionally their interfacial properties (hydrophilicity/hydrophobicity, O 1s/C 1s ratio, pore size and specific surface area) are analyzed, trying to show their influence on the cathode performance in terms of current efficiency. The durability of the cathodes is also examined, along with density functional theory (DFT) studies conducted for the 2e− ORR. Finally, general conclusions and recommendations for future research are presented.