Nickel-iron layered double hydroxides for an improved Ni/Fe hybrid battery-electrolyser.

A Iranzo,F M Mulder

doi:10.1039/d1ma00024a

Abstract

The transition to renewable electricity sources and green feedstock implies the development of electricity storage and conversion systems to both stabilise the electricity grid and provide electrolytic hydrogen. We have recently introduced the concept of a hybrid Ni/Fe battery-electrolyser (battolyser) for this application1. The hydrogen produced during the Ni/Fe cell charge and continued electrolysis can serve as chemical feedstock and a fuel for long-term storage, while the hybrid battery electrodes provide short term storage. Here, we present Ni–Fe layered double hydroxides (NiFe-LDHs) for enhancing the positive electrode performance. The modified Ni(OH)2 material capacity, high rate performance and stability have been tested over a large range of charge rates (from 0.1C to 20C) over 1000 cycles. The Ni–Fe layered double hydroxides allow the capacity per nickel atom to be multiplied by 1.8 in comparison to the conventional β-Ni(OH)2 material which suggests that the nickel content can be reduced by 45% for the same capacity. This reduction of the nickel content is extremely important as this presents the most costly resource. In addition, Fe doped Ni(OH)2 shows improved ionic and electronic conductivity, OER catalytic activity outperforming the benchmark (Ir/C) catalyst, and long term cycling stability. The implementation of this Fe doped Ni(OH)2 material in the Ni/Fe hybrid battery-electrolyser will bring both electrolysis and battery function forward at reduced material cost and energy loss.

Highlights

Annual electricity generation from renewable energy sources is growing rapidly
The Ni–Fe layered double hydroxides allow the capacity per nickel atom to be multiplied by 1.8 in comparison to the conventional b-Ni(OH)[2] material which suggests that the nickel content can be reduced by 45% for the same capacity
– The stabilisation of the alpha/gamma phase couple that allows avoiding the swelling of the electrode and ensuring a better mechanical integrity through the charge, discharge and electrolysis processes

Summary

Introduction

Annual electricity generation from renewable energy sources is growing rapidly. Renewable electricity sources represent 26% of the world’s electricity today and according to the International Energy Agency (IEA) it is expected to reach 30% by 2024.2 IEA expects solar energy to play the largest role in the rise of the renewable energy share. The proposed a-Ni1ÀxFex(OH)[2] material is expected to reduce the cost of materials by increasing the storage capacity per Ni atom, to improve the high rate performance and the energy efficiency of the hybrid Ni/Fe battery by an enhanced OER activity and conductivity (without using Co), and to limit structural fatigue induced by lattice expansions.

Results

Conclusion