# New Insights into the Hydrogen Evolution Mechanism near the Ni/YSZ Triple Phase Boundary during Steam Electrolysis: A Patterned Model Electrode Study

## TL;DR

This study explores how the structure of Ni/YSZ electrodes affects hydrogen production during steam electrolysis, offering insights for improving renewable energy storage.

## Contribution

The paper introduces a patterned model electrode and combines NAP-XPS with electric field modeling to reveal the role of YSZ in hydrogen evolution.

## Key findings

- Surface hydroxylation and electrochemical activity correlate with YSZ domain size and surface area.
- Normalizing current by the electrified catchment area near the TPB improves mechanistic understanding of water electrolysis.
- Optimized structural parameters for enhanced hydrogen evolution reaction performance are identified.

## Abstract

Solid oxide cell technologies play a crucial role in
climate change
mitigation by enabling the reversible storage of renewable energy.
Understanding the electrochemical high-temperature reaction mechanisms
and the catalytic role of the electrode and electrolyte materials
is essential for advancing power-to-H2 technologies. Despite
its significance, limited in situ spectroscopic research
focusing on nickel and yttria-stabilized zirconia (Ni/YSZ) is available.
We employ near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS)
to investigate 2D porous Ni/YSZ model electrodes with variable YSZ
domain sizes and triple phase boundary (TPB) lengths. Focusing on
the hydrogen evolution reaction (HER), we provide a mechanistic explanation
for why surface hydroxylation and electrochemical activity are correlated
with the YSZ surface area and YSZ domain size and unravel the specific
mechanistic role of the YSZ surface. A direct comparison of normalization
of the measured total electrolysis current to the purely geometrical
length of the TPB vs an electrified “catchment area”
next to the TPB, exhibiting strong enough electric fields, is the
key to a correct quantitative description of the individual elementary
steps of water electrolysis on Ni/YSZ. By combining electrochemical
impedance spectroscopy, NAP-XPS, and electric field modeling, the
local water reduction process near the TPB can be described, indicating
optimized structural parameters for improved HER performance.