Harnessing AEM Electrolyzer-Level Performance through Strategically Designing the Electronic Structure of Electrocatalysts, Enabling Dynamic Functional Switching

The
anion exchange membrane water electrolyzer (AEMWE)
is a promising
technology for cost-effective hydrogen production. To promote its
development and adoption, targeted efforts are focused on finding
non-platinum group metal (non-PGM) electrocatalysts that efficiently
facilitate the hydrogen evolution reaction (HER) and the oxygen evolution
reaction (OER). Nickel sulfides (NiS) are effective OER catalysts;
however, they suffer due to leaching-related instability at electrolyzer
stack operational conditions. We introduce a rational non-PGM design
that enhances stability during the OER while excelling at the HER,
showcasing molecular-level insights for a scalable AEMWE zero-gap
stack device. NiS coating is applied to the Al-metal–organic
framework supported by 3D porous nickel foam (NSMA), leading to charge
localization at the interface, which helps in OER by requiring only
322 millivolts at 100 mA cm–2. The main innovation
in the NSMA design is a controlled electroreduction process that converts
the Millerite phase into Ni3S2, a catalyst (rNSMA).
This transformation leads to charge delocalization at the surface
and a low overpotential of −80 mV at −100 mA cm–2 for the HER. In a full cell, this catalyst duo requires
an overpotential of 1.49 V, outperforming the commercial Pt/Ru catalyst
pair at 1.58 V. In a scaled-up 12.96 cm2 AEM electrolyzer
single-cell stack, current density rose from 398 to 1062 mA/cm2, maintained for over 100 h at high temperatures, achieving
99% Faradaic efficiency and 100% hydrogen purity. The AEM electrolyzer
cell shows a good energy efficiency of 45.50 kWh/kg and a cell efficiency
of 86.59%. Detailed studies, including DFT analyses, revealed that
electronic structure modification enhances charge delocalization,
driving its impressive performance on an industrially significant
scale.