Ultrathin, large area β-Ni(OH)2 crystalline nanosheet as bifunctional electrode material for charge storage and oxygen evolution reaction.

[Display omitted] • Large area, 2D β-Ni(OH) 2 , < 3 nm thin nanosheets synthesized at water–air interface. • Device shows 820 mAh.cm−3 capacity with 70% retention after 30,000 cycles. • Device achieved ultrahigh energy density of 0.33 Wh.cm−3 at 275.86 W.cm −3. • β- Ni(OH) 2 shows enhanced OER activity η 10 :308 mV with Tafel value of 42 mV dec-1. • After charge storage & OER, XPS analysis confirms structural stability of the film. Bifunctional electrode materials are highly desirable for meeting increasing global energy demands and mitigating environmental impact. However, improving the atom-efficiency, scalability, and cost-effectiveness of storage systems, as well as optimizing conversion processes to enhance overall energy utilization and sustainability, remains a significant challenge for their application. Herein, we devised an optimized, facile, economic, and scalable synthesis of large area (cm2), ultrathin (∼2.9 ± 0.3 nm) electroactive nanosheet of β-Ni(OH) 2, which acted as bifunctional electrode material for charge storage and oxygen evolution reaction (OER). The β-Ni(OH) 2 nanosheet electrode shows the volumetric capacity of 2.82 Ah.cm−3(0.82 µAh.cm−2) at the current density of 0.2 mA.cm −2. The device shows a high capacity of 820 mAh.cm−3 with an ultrahigh volumetric energy density of 0.33 Wh.cm−3 at 275.86 W.cm −3 along with promising stability (30,000 cycles). Furthermore, the OER activity of ultrathin β-Ni(OH) 2 exhibits an overpotential (η 10) of 308 mV and a Tafel value of 42 mV dec-1 suggesting fast reaction kinetics. The mechanistic studies are enlightened through density functional theory (DFT), which reveals that additional electronic states near the Fermi level enhance activity for both capacitance and OER. [ABSTRACT FROM AUTHOR]