# Flexible Bifunctional Electrode for Alkaline Water Splitting with Long-Term Stability

## TL;DR

A new flexible electrode made of carbon nanotubes and nickel oxide quantum dots efficiently splits water in alkaline conditions with long-term stability.

## Contribution

A novel flexible bifunctional electrode (NiO@CNTR) is developed for efficient and stable alkaline water splitting with low catalyst loading.

## Key findings

- The NiO@CNTR electrode shows strong bifunctional activity for hydrogen and oxygen evolution reactions in alkaline electrolytes.
- The electrode retains nearly 100% of its initial current after 100 hours of water-splitting operation.
- It achieves a low cell potential of 1.81 V with significantly reduced nickel oxide loading compared to existing catalysts.

## Abstract

Progress in electrochemical
water-splitting devices as
future renewable
and clean energy systems requires the development of electrodes composed
of efficient and earth-abundant bifunctional electrocatalysts. This
study reveals a novel flexible and bifunctional electrode (NiO@CNTR) by hybridizing macroscopically assembled
carbon nanotube ribbons (CNTRs) and
atmospheric plasma-synthesized NiO quantum dots (QDs) with varied
loadings to demonstrate bifunctional electrocatalytic activity for
stable and efficient overall water-splitting (OWS) applications. Comparative
studies on the effect of different electrolytes, e.g., acid and alkaline,
reveal a strong preference for alkaline electrolytes for the developed NiO@CNTR electrode, suggesting its bifunctionality
for both HER and OER activities. Our proposed NiO@CNTR electrode demonstrates significantly enhanced overall catalytic
performance in a two-electrode alkaline electrolyzer cell configuration
by assembling the same electrode materials as both the anode and the
cathode, with a remarkable long-standing stability retaining ∼100%
of the initial current after a 100 h long OWS run, which is attributed
to the “synergistic coupling” between NiO QD catalysts
and the CNTR matrix. Interestingly, the developed electrode exhibits
a cell potential (E10) of only 1.81 V
with significantly low NiO QD loading (83 μg/cm2)
compared to other catalyst loading values reported in the literature.
This study demonstrates a potential class of carbon-based electrodes
with single-metal-based bifunctional catalysts that opens up a cost-effective
and large-scale pathway for further development of catalysts and their
loading engineering suitable for alkaline-based OWS applications and
green hydrogen generation.