# Balance between FeIV–NiIV synergy and Lattice Oxygen Contribution for Accelerating Water Oxidation

## TL;DR

This study explores how adding aluminum to a nickel-iron catalyst improves its efficiency and stability for water splitting, a key process for clean hydrogen production.

## Contribution

The paper reveals a new mechanism where FeIV–NiIV synergy enhances OER activity while suppressing lattice oxygen contribution to improve stability.

## Key findings

- Al doping increases Ni valence state, boosting OER activity from 277 mV to 238 mV at 10 mA cm–2.
- Al doping reduces lattice oxygen contribution, improving operational stability despite higher NiIV content.
- Enhanced OER activity is attributed to increased exchange energy from FeIV–NiIV intersite hopping.

## Abstract

Hydrogen obtained
from electrochemical water splitting
is the most
promising clean energy carrier, which is hindered by the sluggish
kinetics of the oxygen evolution reaction (OER). Thus, the development
of an efficient OER electrocatalyst using nonprecious 3d transition
elements is desirable. Multielement synergistic effect and lattice
oxygen oxidation are two well-known mechanisms to enhance the OER
activity of catalysts. The latter is generally related to the high
valence state of 3d transition elements leading to structural destabilization
under the OER condition. We have found that Al doping in nanosheet
Ni–Fe hydroxide exhibits 2-fold advantage: (1) a strong enhanced
OER activity from 277 mV to 238 mV at 10 mA cm–2 as the Ni valence state increases from Ni3.58+ to Ni3.79+ observed from in situ X-ray absorption
spectra. (2) Operational stability is strengthened, while weakness
is expected since the increased NiIV content with 3d8L2 (L denotes O 2p hole) would lead to structural
instability. This contradiction is attributed to a reduced lattice
oxygen contribution to the OER upon Al doping, as verified through in situ Raman spectroscopy, while the enhanced OER activity
is interpreted as an enormous gain in exchange energy of FeIV–NiIV, facilitated by their intersite hopping.
This study reveals a mechanism of Fe–Ni synergy effect to enhance
OER activity and simultaneously to strengthen operational stability
by suppressing the contribution of lattice oxygen.