Phosphine plasma activation of α-Fe2O3 for high energy asymmetric supercapacitors

Abstract We report a phosphine (PH 3 ) plasma activation strategy for significantly boosting the electrochemical performance of supercapacitor electrodes. Using Fe 2 O 3 as a demonstration, we show that the plasma activation simultaneously improves the conductivity, creates atomic-scale vacancies (defects), as well as increases active surface area, and thus leading to a greatly enhanced performance with a high areal capacitance of 340 mF cm −2 at 1 mA cm −2 , compared to 66 mF cm −2 of pristine Fe 2 O 3 . Moreover, the asymmetric supercapacitor devices based on plasma-activated Fe 2 O 3 anodes and electrodeposited MnO 2 cathodes can achieve a high stack energy density of 0.42 mW h cm −3 at a stack power density of 10.3 mW cm −3 along with good stability (88% capacitance retention after 9000 cycles at 10 mA cm −2 ). Our work provides a simple yet effective strategy to greatly enhance the electrochemical performance of Fe 2 O 3 anodes and to further promote their application in asymmetric supercapacitors.