General Approach to Synthesize Multilayer Graphitic Carbon- Nanotube-Encapsulated NiCo Alloys as Trifunctional the Role of

Designing effective multifunctional electrocatalysts with robust activity and durability is crucial for developing different electrochemical energy storage/conversion devices. In this study, we established a general approach to synthesize a multilayer N-doped graphitic carbon nanotube (CNT)-encapsulated NiCo alloy, which exhibits robust trifunctional electrocatalytic activity toward three fundamental electrochemical reactions: oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER). Remarkably, the synthesized NiCo alloy with melamine as the N-dopant (NiCo-M) exhibits admirable trifunctional activity with a low overpotential of 109 mV for HER and 295 mV for OER to achieve the benchmark current density of 10 mA cm-2 as well as superior ORR performance (onset: 0.96 V; E1/2: 0.856 V) in alkaline medium. More importantly, the NiCo-M electrocatalyst possesses excellent oxygen electrocatalytic activity with a small potential difference (Delta E) of 0.669 V, which is very close to that of the state-of-the-art Pt/C-RuO2 (0.651 V) couple. Such overwhelming performances stem from the presence of sufficient active sites and the formation of a unique N-doped graphitic CNT-like structure, which encourages electronic structure modulation as well as synergism for improved trifunctional electrocatalytic activities. Moreover, the catalyst shows outstanding electrochemical stability with a negligible decay of overpotential or E1/2 values after exhaustive CV cycles for HER, OER, and ORR. This is attributed to the encapsulation of the NiCo alloy into a N-doped multilayer graphitic carbon shell. The present study will offer a general approach to rationally synthesize robust trifunctional for-efficient electrochemical devices.

Automated summary

Designing effective multifunctional electrocatalysts is crucial for developing electrochemical energy storage/conversion devices. In this study, a general approach to synthesize a multilayer N-doped graphitic carbon nanotube (CNT)-encapsulated NiCo alloy with robust trifunctional electrocatalytic activity is established. The synthesized NiCo alloy exhibits admirable performance in oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER), with excellent stability.