Fig. 5: Electrochemical responses of GA–Fe and the composition of its product after electrochemical oxidation.

a Successive CV curves investigating redox behavior of fresh GA–Fe in electrolyte solution (pH = 6.5). The CV was originally swept from + 0.1 to – 0.5 V, followed by five complete cycles. b UV-Vis absorption spectra of GA–Fe sample before and after electrochemical oxidation enabled by successive CV scanning. c CA profiles of electrolyte solution containing fresh GA–Fe in response to seven consecutive periods of double potential step transitions (high potential: 0.90 V; low potential: 0.15 V). d Comparison among limited current responses of electrolyte solutions containing fresh GA–Fe or Fe³⁺ when a half-period of continuous high potential (0.90 V) actions during the successive double potential step transitions of CA (GA–Fe: in the first and seventh periods marked in panel (c); Fe³⁺: in the seventh period marked in Supplementary Fig. 20b). e The electrochemical oxidation product of GA–Fe after CA measurement in (c) (i.e., GA_ox–Fe) further underwent a second round of CA measurement (high potential: 0.90 V; low potential: −0.45 V; seven successive cycles). f Comparison among limited current responses of electrolyte solutions containing GA_ox–Fe or Fe³⁺ under the action of a half-period of continuous high potential (0.90 V) during the new round of double potential step transitions (GA–Fe: in the first and seventh period marked in panel (e); Fe³⁺: in the seventh period marked in Supplementary Fig. 20d). As this round of CA is catalytic, the limited current response of GA_ox–Fe is nearly not changed during seven consecutive periods of double potential step transitions. g Raman spectrum of electrochemically oxidated GA–Fe nanoparticles after two rounds of CA measurements. h Fe 2p spectrum of XPS spectra of electrochemically oxidated GA–Fe nanoparticles after two rounds of CA measurements. Source data are provided as a Source Data file.