In situ formation of heterojunction of thiophene-based metal–organic frameworks with carbon dots for efficient overall water splitting and supercapacitor applications†

Investigating a single multifunctional electrode in an integrated device, such as self-powered overall water splitting (OWS), is extremely valuable since it may substantially decrease the system complexity and expense. Hence, a full rice-spike-like 400N-CDs/FeNi-TDC nanoarray combining N-hybridized carbon dots (N-CDs) and FeNi-TDC with 2,5-thiophenedicarboxylic acid (H₂TDC) as ligands is constructed on the surface of a nickel foam by a one-pot solvothermal method for OWS and supercapacitor applications. Based on interface-heterojunction engineering, the morphology and electronic environment at the active sites of the nanomaterial successfully controlled by N-CDs and the heterojunction synergistically promoted efficient catalysis. The optimized 400N-CDs/FeNi-TDC electrode exhibits a 209 mV overpotential and a Tafel slope of 18.91 mV dec⁻¹ at 10 mA cm⁻² during the oxygen evolution reaction (OER) activity, as well as a low overpotential of 99 mV to reach 10 mA cm⁻² with a Tafel slope of 77.01 mV dec⁻¹ in the hydrogen evolution reaction (HER). As the positive electrode of the supercapacitor, the high specific capacitance of 400N-CDs/FeNi-TDC is 2388 F g⁻¹ at 1 A g⁻¹. The assembled self-powered OWS device uses the 400N-CDs/FeNi-TDC‖AC/NF with pre-charged 3 V as the power supply to achieve simultaneous green hydrogen and oxygen production for ∼4 min. This research provides a new platform to build state-of-the-art and sustainable energy conversion and storage devices.