Triboelectric nanogenerators powered electrodepositing tri-functional electrocatalysts for water splitting and rechargeable zinc-air battery: A case of Pt nanoclusters on NiFe-LDH nanosheets

Abstract

Abstract Designing highly efficient electrocatalysts with superior performance on electrochemical water splitting and rechargeable metal-air batteries is an urgent and challenging task due to required large overpotentials. A pulsed direct current with high voltage produced by a layered triboelectric nanogenerator (TENG) provides a novel type of power sources to electrodeposit sub-2 nm Pt nanoclusters onto NiFe-LDH nanosheets in the absence of any capping reagents to improve hydrogen evolution reaction (HER) activity and to electronically reduce part of Fe3+ cations in the lattice of NiFe-LDH to Fe2+ species to enhance oxygen evolution reaction (OER) activity. The particle size of Pt nanoclusters could be easily tuned from 0.8 nm to 1.2 nm by alternating the working frequency of the layered TENG. By loading sub-2 nm Pt nanoclusters onto NiFe-LDH (Pt–NiFe-LDH), the HER overpotential drops from 345 mV to 86 mV at a current density of 50 mA cm−2 in alkaline electrolyte. The synergistic effect between Pt nanoclusters and NiFe-LDH nanosheets on enhancing the cleavage of HO–H bond and recombination of hydrogen intermediates to form molecular hydrogen dramatically improves the HER activity. Meanwhile, benefiting from tuning the local atomic structure and crystal defects by reducing Fe3+ to Fe2+, NiFe-LDH nanosheets demonstrates enhanced OER activity. The deposited sub-2 nm Pt nanoclusters also produces elevated oxygen reduction reaction (ORR) activity with a half-wave potential of 0.84 V (vs RHE). Hence, the as-prepared Pt–NiFe-LDH catalysts exhibits tri-functional properties towards HER, ORR and OER and could be used as the electrode catalysts for overall electrocatalytic water splitting and rechargeable zinc-air batteries. With the optimal catalyst (Pt–NiFe-LDH-0.5-12) as the electrode for overall water splitting, the potential difference between OER and HER drops to 1.63 V at a current density of 50 mA cm−2, much lower than that of the mixed noble-metal catalysts (Pt/C and RuO2, 1.98 V). As an air electrode of rechargeable zinc-air batteries, Pt–NiFe-LDH-0.5-12 exhibits much better performance than that of bare NiFe-LDH in terms of higher open-circuit voltage, higher round-trip efficiency and durability.