Manganese and Nitrogen Doped Biomass-Based Activated Carbons As Electrocatalysts for Oxygen Reduction and Water Splitting

In this study, an efficient manganese (Mn) and nitrogen (N) co-doped carbon materials were prepared using the three raw materials, namely alder charcoal (Mn-N-C AC ), hydrothermally carbonised birch wood (Mn-N-C W ), and black liquor (Mn-N-C BL ). At first, biomass-based activated carbon materials were synthesized. Mn and N were co-doped in one step using the reaction mixture containing Mn 2+ ions source, activated carbon material, and dicyandiamide (DCDA) in dimethylformamide (DMF). DMF was evaporated and the mixture was treated for 60 min at a temperature of 800 ºC. The specific surface area, morphology, structure, and composition of Mn-N-C were determined using BET, TEM, XPS, Raman, XRD, and ICP-OES. Activity of resulted Mn-N-C materials was evaluated for oxygen reduction (ORR) as well as for hydrogen and oxygen evolution (HER and OER) using linear-sweep voltammetry (LSV) with a rotating disk electrode (RDE) in alkaline media. It was found that all Mn-N-C materials had a high specific surface area in the range of approximately of 1800 to 2200 m 2 g -1 but the Mn-N-C BL presented a higher contribution of the mesopores in comaparison to Mn-N-C AC and Mn-N-C W which are similar. All synthesized Mn-N-C materials exhibit excellent electrocatalytic activity for ORR with the onset and half-wave potentials of approximately 0.88‒0.90 and 0.80‒0.84 V, respectively, showing the 4e ‒ electrons transfer path in 0.1 M KOH solution. The Mn-N-C materials also show enhanced activity for HER and OER in alkaline media. Acknowledgment The “Sustainably Produced Carbon Nanomaterials for Energy Applications (SuNaMa)” benefits from a 988000 € grant from Iceland, Liechtenstein, and Norway through the EEA Grants. The aim of the project is to develop innovative, high-performance, highly conductive, electrocatalytically active, durable, cost-effective, and high surface area nanocarbon materials. Project contract with the Research Council of Lithuania (LMTLT) No. is S-BMT-21-12 (LT08-2-LMT-K-01-055).