Fe-functionalised N-doped Ti3C2Tz MXene for the alkaline oxygen reduction reaction

Abstract

Alkaline fuel cells are promising technologies to decarbonise current energy systems. One of the main advantages they present is that non-expensive metals can be used as catalysts, reducing overall manufacturing costs. A promising family of electrocatalysts for the oxygen reduction reaction, which is the most difficult reaction in most fuel cell systems, are Fe-N-C catalysts, which have shown performance close to platinum-based catalysts. Coupling these with MXenes is a promising alternative, as MXenes can act as supports that will homogeneously disperse the metal species and catalyse the formation of carbon species that increase performance for the ORR. In this paper, we intercalate Fe species and urea in Ti₃C₂T_z MXene and fully characterise the materials using a range of techniques, including Mössbauer spectroscopy. The materials are then tested for the ORR in alkaline media, with one sample (Ti₃C₂-U50-Fe-800) showing excellent performance and stability in 0.1 M KOH, including an onset potential of 0.93 V vs RHE, an electron transfer number of 3.8 at 0.8 V vs RHE, a Tafel slope of 66 mV/dec, and a small shift of 37 mV for the half-wave potential for linear sweep voltammetry before and after 2,000 cycles. This performance is attributed to the high nitrogen content that favourably forms pyridinic N species on this sample, and the MXene support, which disperses the Fe species and catalyses the formation of favourable carbon materials.