Three-dimensional CoNi alloy nanoparticle and carbon nanotube decorated N-doped carbon nanosheet arrays for use as bifunctional electrocatalysts in wearable and flexible Zn-air batteries

A novel three-dimensional (3D) bifunctional electrocatalyst, CoNi alloy nanoparticle and carbon nanotube decorated N-doped carbon nanosheet arrays on carbon cloth (CoNi alloy/NCNSAs/CC) derived from polymetallic organic frameworks, is firstly prepared. The CoNi alloy/NCNSAs/CC-800 fabricated by pyrolyzing at 800 °C exhibits an oxygen reduction reaction (ORR, limiting current density) of 6.5 mA cm−2 and a superior oxygen evolution reaction (OER, at 10 mA cm−2) of 1.51 V, as well as a smaller potential difference of 0.676 V between OER and ORR half-wave potential, outperforming previous self-supporting cathodes. Flexible Zn-air batteries (FZABs) assembled with the CoNi alloy/NCNSAs/CC-800 exhibit higher energy density (98.8 mW cm−2) and higher capacity (879 mAh g−1), as well as excellent mechanical cycle ability (lower voltage gap of 0.66 V during the charge/discharge cycles at flat and folded state), significantly outstripping all other FZABs with self-supporting electrodes currently reported. Such a remarkable performance is ascribed to the 3D hierarchical nanostructure which promotes mass transport, the higher graphitization facilitating electronic mobility and the evenly dispersed active sites which accelerate kinetic reactions. So CoNi alloy/NCNSAs/CC-800 is a promising cathode candidate for ideal wearable energy devices and has great potential application in the field of electrochemical energy storage and conversion.