Efficient water and urea electrolysis with bimetallic yolk-shell nanoparticles
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Electrolytic hydrogen production powered by renewable energy is seen
as an environmentally friendly means to ameliorate global climate and
energy problems. In the journal Angewandte Chemie, a research
team has now introduced a novel and inexpensive material for electrodes
that may provide for highly efficient, energy-saving hydrogen
production: porous, phosphorized CoNi2S4 yolk-shell nanospheres.
Both half reactions of water electrolysis—hydrogen and oxygen
evolution—are unfortunately slow and require a lot of power.
Catalytically effective electrodes, particularly those based on precious
metals, can accelerate the electrochemical processes and improve their
energy efficiency. However, their large-scale use is impeded by high
costs, limited abundance, and low stability. Alternatives based on
abundant, inexpensive metals usually do not work satisfactorily for both
half reactions.
A team led by Shuyan Gao (Henan Normal University, China) and Xiong
Wen (David) Lou (Nanyang Technological University, Singapore) has now
developed a novel, inexpensive, multifunctional electrode material based
on cobalt (Co) and nickel (Ni) for efficient electrocatalytic hydrogen
production. To make the material, nanospheres made of
cobalt–nickel–glycerate are subjected to combined hydrothermal
sulfidation and gas-phase phosphorization. This forms objects called
yolk-shell nanoparticles made of phosphorus-doped cobalt–nickel–sulfide
(P-CoNi2S4). These are tiny spheres with a compact
core and a porous shell with a space in between—much like an egg whose
yolk is surrounded by the egg white and so does not touch the shell.
Phosphorus doping increases the proportion of Ni3+ relative to Ni2+
in the hollow particles and allows for faster charge transfer, causing
the electrocatalytic reactions to run faster. The material can be used
as either an anode or a cathode, and demonstrates high activity and
stability in the production of hydrogen and oxygen in the electrolysis
of water.
To reduce the overall voltage of the electrolysis cell, hybrid
electrolysis concepts are also being researched. For example, instead of
being coupled to the production of oxygen, hydrogen production could be
coupled to the oxidation of urea, which requires significantly less
energy. Sources of urea could include waste streams from industrial
syntheses as well as sanitary sewage. The new nanoparticles are also
very useful for this half reaction.
Both water and urea electrolysis require comparatively low cell voltage (1.544 V or 1.402 V, respectively, at 10 mA cm–2
over 100 hours). This makes the new bimetallic yolk-shell particles
superior to most known nickel–sulfide- and even precious-metal-based
electrocatalysts. They present a promising approach for electrochemical
hydrogen production, as well as for the treatment of urea-containing
wastewater.
(2941 characters)
About the Author
Xiong Wen (David)
Lou is the Cheng Tsang Man Chair Professor in Energy at Nanyang
Technological University, Singapore. His current research is focused on
the design and synthesis of nanostructured materials for different
applications in batteries, electrocatalysis, and photocatalysis.
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Permalink to the original article: https://doi.org/10.1002/anie.202107231
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