2 research outputs found
Enhanced Dispersion and Stability of Petroleum Coke Water Slurries via Triblock Copolymer and Xanthan Gum: Rheological and Adsorption Studies
The rheology of petroleum coke (petcoke)
water slurries was investigated
with a variety of nonionic and anionic dispersants including poly(ethylene
oxide) (PEO)-<i>b</i>-poly(propylene oxide) (PPO)-<i>b</i>-PEO triblock copolymers (trade name: Pluronic, BASF),
poly(vinyl alcohol) (PVA), polyvinylpyrrolidone (PVP), poly(ethylene
oxide) (PEO), poly(carboxylate acid) (PCA), sodium lignosulfonate
(SLS), and poly(acrylic acid) (PAA). Each effective dispersant system
shared very similar rheological behavior to the others when examined
at the same volume fraction from its maximum petcoke loading. Triblock
copolymer, Pluronic F127 (F127), was found to be the best dispersant
by comparing the maximum petcoke loading for each dispersant. The
yield stress was measured as a function of petcoke loading and dispersant
concentration for F127, and a minimum dispersant concentration was
observed. An adsorption isotherm and atomic force microscopy (AFM)
images reveal that this effective dispersion of petcoke particles
by F127 is due to the formation of a uniform monolayer of brushes
where hydrophobic PPO domains of F127 adhere to the petcoke surface,
while hydrophilic PEO tails fill the gap between petcoke particles.
F127 was then compared to other Pluronics with various PEO and PPO
chain lengths, and the effects of surface and dispersant hydrophilicity
were examined. Finally, xanthan gum (XG) was tested as a stabilizer
in combination with F127 for potential industrial application, and
F127 appears to break the XG aggregates into smaller aggregates through
competitive adsorption, leading to an excellent degree of dispersion
but the reduced stability of petcoke slurries
Surface-Modified Carbon Nanotubes with Ultrathin Co<sub>3</sub>O<sub>4</sub> Layer for Enhanced Oxygen Evolution Reaction
Alkaline
water electrolysis is a vital technology for sustainable
and efficient hydrogen production. However, the oxygen evolution reaction
(OER) at the anode suffers from sluggish kinetics, requiring overpotential.
Precious metal-based electrocatalysts are commonly used but face limitations
in cost and availability. Carbon nanostructures, such as carbon nanotubes
(CNTs), offer promising alternatives due to their abundant active
sites and efficient charge-transfer properties. Surface modification
of CNTs through techniques such as pulsed laser ablation in liquid
media (PLAL) can enhance their catalytic performance. In this study,
we investigate the role of surface-modified carbon (SMC) as a support
to increase the active sites of transition metal-based electrocatalysts
and its impact on electrocatalytic performance for the OER. We focus
on Co3O4@SMC heterostructures, where an ultrathin
layer of Co3O4 is deposited onto SMCs using
a combination of PLAL and atomic layer deposition. A comparative analysis
with aggregated Co3O4 and Co3O4@pristine CNTs reveals the superior OER performance of Co3O4@SMC. The optimized Co3O4@SMC exhibits a 25.6% reduction in overpotential, a lower Tafel slope,
and a significantly higher turnover frequency (TOF) in alkaline water
splitting. The experimental results, combined with density functional
theory (DFT) calculations, indicate that these improvements can be
attributed to the high electrocatalytic activity of Co3O4 as active sites achieved through the homogeneous distribution
on SMCs. The experimental methodology, morphology, composition, and
their correlation with activity and stability of Co3O4@SMC for the OER in alkaline media are discussed in detail.
This study contributes to the understanding of SMC-based heterostructures
and their potential for enhancing electrocatalytic performance in
alkaline water electrolysis