Additive free Co-lean ternary NiCoAl/Ni foam electrode for high-efficiency energy storage and low-grade heat harvesting

Abstract

This work aims to develop a sustainable, additive-free, and Co-lean ternary NiCoAl layered double hydroxide (NCA) electrode capable of delivering high-performance electrochemical energy storage and low-grade heat harvesting. A Ni-rich, Co-lean NCA was directly grown on nickel foam (NCA/NF) via a simple hydrothermal process, forming 3D hierarchical microflowers composed of ultrathin (27 nm) nanosheets. The optimized Ni : Co : Al ratio (4 : 2 : 1) maximizes Ni²⁺/Ni³⁺ redox activity, stabilizes the LDH lattice through Al³⁺ incorporation, and enhances charge-transfer kinetics via Ni–O–Co interactions. The resulting NCA/NF electrode delivers a specific capacitance of 3346 F g⁻¹ (5019 mF cm⁻²) at 1.5 A g⁻¹ and enables an asymmetric supercapacitor with a specific energy of 55.4 Wh kg⁻¹ at 797.7 W kg⁻¹, retaining 51.1 Wh kg⁻¹ even at 7998.2 W kg⁻¹. Combined with 92% capacity retention over 25 000 cycles, the NCA/NF electrode simultaneously retains specific energy and power capability. This well-balanced energy-power-stability performance is a critical requirement for next-generation high-power electrochemical systems and is rarely achieved in fully additive-free LDH electrodes. In parallel, the NCA/NF electrode functions as an efficient thermoelectrochemical material, achieving a Seebeck coefficient of 5.5 mV K⁻¹ and storing 1.65 J of thermal charge under a modest 0–10 K gradient. This performance has not previously been reported for Ni-based electrodes at such low ΔT. These findings establish Ni-rich, Co-lean NCA/NF as a scalable and sustainable bifunctional electrode platform that unites compositional tuning, structural integrity, and efficient energy storage and conversion capability.