N‐Doped FeS2 Achieved by Thermal Annealing of Anodized Fe in Ammonia and Sulfur Atmosphere: Applications for Supercapacitors

Iron pyrite (FeS2) has attracted intense research interest for low-cost supercapacitor applications due to its improved electrical conductivity in comparison with its oxide counterpart. Herein, we demonstrate a novel strategy for the facile synthesis of N-doped FeS2 nanosphere films on iron substrate, which includes anodization of Fe and subsequent thermal annealing treatment. The rod-like ferrous oxalate films are obtained by anodization of Fe in an oxalic acid electrolyte. Then, nanosphere-like N-doped FeS2 films can be readily achieved through thermal annealing of ferrous oxalate films under ammonia (NH3) atmosphere in the presence of sulfur powder. The N-doped FeS2 electrode fabricated without the need for any binder shows superior rate capability and enhanced specific capacitance compared to the pristine FeS2. The prepared N-doped FeS2 nanosphere electrode displays a high specific capacitance of 238.2 mF cm−2 at 3 mA cm−2 over a potential range of −1.2 to 0 V and good cycling stability with a capacitance retention of 84.3% after 5000 cycles.