che_october-2024 - 8

A low-cost coating system designed to optimize
water electrolysis
S
eemingly small component changes can make a
large impact on the productivity of electrochemistry
systems, such as electrolyzers used for producing
" green " hydrogen. For example, a new
coating technology developed by Oxford nanoSystems
Ltd. (OnS; Abingdon, U.K.; www.oxfordnanosystems.
com), when applied to the electrodes of alkaline electrolyzers,
can boost the electrical current flowing through
the system, thereby increasing the rate of hydrogen production.
" The resulting increase in production capacity
lowers the CAPEX cost of alkaline electrolyzers by over
50%, relative to existing technologies. This very substantially
reduces the cost of producing green hydrogen, "
notes Ian Russell, CEO of OnS.
Historically, alkaline electrolyzers have relied on coating
materials containing expensive platinum-group metals
(PGMs) to enhance performance. However, the OnS
coating, nanoFLUX, provides comparable performance
to PGM-loaded coatings at a lower cost than conventional
nickel-based electrodes, says Russell. Key to this
performance is the coating's dendritic structure that creates
a network of microcavities on the substrate's surface
(photo) that significantly enhances the density of sites
available for bubble formation. Additionally, the highly porous
nature of nanoFLUX facilitates the release of bubbles
and promotes surface re-wetting. This leads to a greater
number of smaller bubbles being generated and expelled
from the coated surface at an accelerated rate, thereby
minimizing resistance and losses due to bubble buildup.
" Bubble release is critical because the electrochemistry
reaction takes place where the liquid electrolyte is
in contact with the solid electrode. Prior to their release
Scaleup underway for super-efficient silver refining
A
significant contributor to the cost, energy consumption
and carbon footprint of silver production
is in the refining steps to remove, recover
and recycle zinc from Parkes Crust silver-zinc
intermetallic compounds.
A fundamental redesign of the silver process to improve
dezincing kinetics - the rate-limiting step in silver
refining - was recently reported in the Journal of Sustainable
Metallurgy. The new Britannia Silver Process
(BSP) introduces a redesigned vacuum dezincing unit
and removes a liquation stage that requires the crust to
be melted and mixed with lead.
" The use of natural-gas heating in the BSP dezincing
process compared to electric-induction operation
used in current processes delivers significant
energy-efficiency improvements. Liquation in the
current process is very energy-intensive, and its replacement
also delivers significant energy-efficiency
gains, " explains Steven King, a principal metallurgist
with the Glencore Group (Baar, Switzerland; www.
glencore.com), who conducted the work along with
Alberto Striolo, professor of chemical engineering at
University College London (UCL; www.ucl.ac.uk) and
University of Oklahoma (Norman; www.ou.edu), at
8
Glencore's Britannia Refined Metals (BRM) facility in
the U.K. The work carried out at BRM was conducted
with a significant emphasis on process safety with
no accidents, despite the experimental nature of the
project, notes King.
In pilot operation, the new process has demonstrated
dezincing kinetics 44% higher than the original process,
as well as a higher purity and recovery efficiency of zinc.
" The pilot plant used to develop the process and validate
performance metrics was a ¼-scale rendition of a
full-scale plant. Development of a demonstration-scale
plant is now in progress. I would consider the dezincing
geometry we have developed to be new and fully original, "
says King. The pilot-scale operation also revealed
a nearly 40% reduction in energy usage and 31% reduction
in Scope 1 carbon emissions, while producing
a silver product of comparable quality to traditional refining
processes.
Another benefit of the BSP is the promise of recycling
and reducing waste, such as slag. " Current processes
dispose of this waste stream. The BSP presents the
opportunity to recycle the flux and direct the zinc oxide/
lead oxide residue to the zinc-recovery processes, "
adds King.
CHEMICAL ENGINEERING WWW.CHEMENGONLINE.COM
OCTOBER 2024
from the electrode surface, gas bubbles form an insulating
layer between solid and liquid, reducing the effective
area of the electrode, " explains Russell.
For electrolyzer applications, the nanoFLUX coating
has been combined with a proprietary non-PGM catalyst
to activate the hydrogen-generation reaction. " The coating
process is based on aqueous electrochemistry. The
principal steps are the electroless deposition and growth
of the nanoFLUX layer, followed by electroplating of the
catalytic later. In addition, there are some surface-cleaning,
preparation and rinsing steps within the overall process, "
says Russell. OnS is currently operating a demonstration
plant with the capability to coat electrodes up to
700 mm in diameter - similar in scale to those used in
commercial systems - with plans to move to commercial
production in 2025.
Oxford nanoSystems
http://www.oxfordnanosystems.com http://www.glencore.com http://www.ucl.ac.uk http://www.ou.edu http://WWW.CHEMENGONLINE.COM
che_october-2024

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