Enhancing OER performance through catalyst-support interaction: A breakthrough in Ni3Fe oxide/pani catalysts

The oxygen evolution reaction (OER) plays a crucial role in various energy conversion technologies, including water splitting and rechargeable metal-air batteries. However, achieving high efficiency and stability in OER catalysts remains a significant challenge. A research team from the Hong Kong Polytechnic University, led by Prof. Liang An, has demonstrated that tuning the catalyst–support interaction in polyaniline-supported Ni₃Fe oxide (Ni₃Fe oxide/PANI) can significantly enhance catalytic performance, paving the way for advanced energy applications.

In this work, researchers successfully engineered a robust hetero-interface between Ni₃Fe oxide and PANI support. This interaction enhances Ni–O covalency via interfacial Ni–N bonds, improving both charge and mass transfer properties. As a result, the Ni₃Fe oxide/PANI catalyst exhibits outstanding OER performance with an overpotential of just 270 mV at 10 mA cm⁻². Moreover, it achieves a remarkable specific activity of 2.08 mA cmECSA⁻² at an overpotential of 300 mV, which is 3.84 times higher than that of Ni₃Fe oxide alone.

The study highlights the importance of structural control in catalyst design. The Ni₃Fe oxide nanoparticles, with an average size of just 3.5 ± 1.5 nm, are uniformly distributed on the amorphous PANI support, forming an optimal hetero-interface. This structure not only boosts electronic interactions but also facilitates charge transport, leading to an improved catalytic process. With a Tafel slope of only 60 mV dec⁻¹, the catalyst showcases excellent reaction kinetics and prolonged OER stability of 150 hours at 10 mA cm⁻².

Additionally, the catalyst’s performance was further analyzed through pH-dependent studies, which confirmed that both Ni₃Fe oxide/PANI and Ni₃Fe oxide followed the lattice oxygen-mediated (LOM) pathway. The Ni₃Fe oxide/PANI catalyst exhibited a reaction order of 0.305, higher than the 0.254 of Ni₃Fe oxide, indicating enhanced Ni–O covalency due to the presence of PANI. These insights demonstrate that the careful selection of a conductive support can significantly impact catalytic efficiency and longevity.

The superior OER activity and durability of Ni₃Fe oxide/PANI catalysts make them highly suitable for practical applications. When integrated into rechargeable Zn-air batteries, the optimized catalyst demonstrates an ultra-long cycle life of over 400 hours at 10 mA cm⁻². It also delivers a low charge voltage of just 1.95 V, significantly outperforming conventional Ni₃Fe oxide and commercial Pt/C-IrO₂ catalysts. The excellent stability and efficiency of the Ni₃Fe oxide/PANI composite highlight its potential for next-generation energy storage and conversion devices.

Further investigation into the reaction mechanism reveals that Ni₃Fe oxide/PANI follows the lattice oxygen-mediated (LOM) pathway, as demonstrated by its pH-dependent OER activity. The incorporation of the PANI support enhances Ni–O covalency through interfacial Ni–N bonds, accelerating charge and mass transfer. Electrochemical impedance spectroscopy (EIS) analysis indicates that Ni₃Fe oxide/PANI exhibits lower charge transfer impedance and phase angles compared to Ni₃Fe oxide alone, confirming improved electron transport properties.

Operando EIS measurements further highlight that the charge transfer resistance of Ni₃Fe oxide/PANI is significantly lower than that of Ni₃Fe oxide, Ni oxide/PANI, and Fe oxide/PANI, indicating a superior mass transfer process. The phase angle and frequency analysis reveal that Ni₃Fe oxide/PANI has a phase angle of 5.9° and a frequency of 3.9 Hz at 1.62 V versus RHE, significantly lower than the 8.5° and 10.3 Hz of Ni₃Fe oxide. This suggests a more efficient electron transport mechanism, facilitated by the conductive PANI support.

Additionally, during OER, the surface of Ni₃Fe oxide is electrochemically converted into a Ni_0.75Fe_0.25OOH layer, and Ni–N bonds are formed at the hetero-interface of Ni₃Fe oxide and PANI support. These bonds help increase the valence state of Ni atoms and enhance electron transfer to the conductive PANI support, thereby improving the overall reaction kinetics and catalytic activity.

With its impressive OER activity, superior electron transfer efficiency, and outstanding performance in Zn-air batteries, this work sets a new benchmark in catalyst design. It demonstrates the crucial role of catalyst-support interactions in electrochemical energy conversion and provides valuable insights for the future development of high-performance energy catalysts.