Novel solid-state glycine-nitrate combustion for controllable synthesis of hierarchically porous Ni monolith Qin Guo, Ying Zhao, Jiatu Liu, Cheng Ma, Hangyu Zhou, Boyun Huang and Weifeng Wei * State Key Lab for Powder Metallurgy, Central South University, Changsha, Hunan, P.R.China 410083. Abstract:We demonstrate a novel solid-state glycine-nitrate route for not only the scalable combustion synthesis of hierarchically porous Ni monolith, but also control over impurities, microstructure topography and size. The as-synthesized porous Ni monolith may find instant applications as electrode current collectors, catalyst and catalyst substrates or sensors. Key words: porous metal foam; combustion synthesis; hierarchical pore; supercapacitor; energy density Porous metal foam, due to its excellent electronic conductivity, high permeability, low density, and high specific surface area, has been widely employed as electrode backbone, catalysts and catalyst substrates, and sensors 1-7 . Recently, its important role has been highlighted by the surge of binder-free high- performance supercapacitors and lithium ion batteries (LIBs) electrodes: direct deposit of active material on three-dimensional conductive current collector for both enhanced electronic conductivity and simplified electrode preparation procedure 4, 5, 8-10 . Although direct deposit has been easily achieved, the supporting backbone was obtained by elaborate process 11 even with highly toxic precursors in the case of Incofoam® Ni foam 12 ; still, the large pore size (200μm to 2mm) and consequent low specific surface area of the inactive backbone may counteract the specific capacity and energy density of the electrode as a whole 6, 13 . Thus, alternative porous Ni foam with optimized pore structure by facile method would be most enticing not only for higher energy density for free-standing advanced electrodes but also its low-cost application in fields as energy storage, catalyst and sensors. Glycine-nitrate combustion (GNC), a novel illustration of sustainable redox reaction and propellant chemistry, has proved to be a simple but cost-effective method for scalable synthesis of porous and fine advanced ceramics, catalysts and nanomaterials 14, 15 . Typically, an oxidizer (O) and a fuel (F) are first mixed in solution. When heated, the solution turns to vicious gel and begins to foam after gelation. Then the redox reaction initiates at critical ignition temperature (Tig) and sustains due to intensive heat release. Meanwhile, solid-state products are released, sintered into different microstructure and made porous by the gaseous ones 14- 17 . Solution GNC received intensive attention when Avarma etal 18 obtained transition metal/alloy/cermet rather than oxides by tuning F/O ratio, of which the mechanism has been revealed through detailed studies by Manukyans etal 19, 20 . * Email: [email protected]Recently, modified combustion or redox method has been employed to first obtain nanostructured porous metal powder, followed by post-shaping into monolith which began to serve as current collector of supercapacitor and LIB 13, 21 . However, the as-prepared metal backbone may suffer from friable problem and increased contact resistance compared with its continuous counterparts. Till now, continuous porous metal monolith with considerable strength has not yet been realized by this simple and cost-effective combustion method due to the following reasons: (1) foaming problem during gelation makes it difficult to achieve uniform density of the products; (2) much gas released within such a short time gives the combustion spraying nature; (3) the instant and spraying nature makes the sintering of products insufficient to achieve reliable strength. Based on previous pioneering studies, we report in this communication the successful synthesis of continuous hierarchically-porous Ni monolith by a novel solid-state GNC: before heated to Tig, the viscous gel with high F/O ratio was sufficiently dried to solid- state which was then shaped and ignited in solid state under mechanical confinement. By integrating solution GNC into solid-state combustion, we achieved such merits as follows: (1) molecular-level blending of simple chemical reagents as in solution combustion was inherited rather than expensive micro-scale metal or non-metal powders mixed by tedious ball milling in solid-state combustion; (2) foaming problem in solution combustion was annulled by subsequent shaping process which not only promises uniform density of products but also steady self-propagating combustion behaviour as in conventional solid-state combustion; (3) less gas especially water would burst out and breach the architecture after intensified drying. To obtain continuous monolith, we highlighted the premised role of released gas compared with conventional gasless solid-state combustion; (4) up- scale of GNC was well weaved into mature procedure as shaping and post-processing could be omitted.
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Novel solid-state glycine-nitrate combustion for controllable
synthesis of hierarchically porous Ni monolith
Qin Guo, Ying Zhao, Jiatu Liu, Cheng Ma, Hangyu Zhou, Boyun Huang and Weifeng Wei *
State Key Lab for Powder Metallurgy, Central South University,
Changsha, Hunan, P.R.China 410083.
Abstract:We demonstrate a novel solid-state glycine-nitrate route for not only the scalable
combustion synthesis of hierarchically porous Ni monolith, but also control over impurities,
microstructure topography and size. The as-synthesized porous Ni monolith may find instant
applications as electrode current collectors, catalyst and catalyst substrates or sensors.
Key words: porous metal foam; combustion synthesis; hierarchical pore; supercapacitor; energy density
Porous metal foam, due to its excellent electronic
conductivity, high permeability, low density, and high
specific surface area, has been widely employed as
electrode backbone, catalysts and catalyst substrates,
and sensors1-7. Recently, its important role has been
highlighted by the surge of binder-free high-
performance supercapacitors and lithium ion batteries
(LIBs) electrodes: direct deposit of active material on
three-dimensional conductive current collector for both
enhanced electronic conductivity and simplified
electrode preparation procedure4, 5, 8-10. Although direct
deposit has been easily achieved, the supporting
backbone was obtained by elaborate process11 even
with highly toxic precursors in the case of Incofoam®
Ni foam12; still, the large pore size (200μm to 2mm)
and consequent low specific surface area of the inactive
backbone may counteract the specific capacity and
energy density of the electrode as a whole6, 13. Thus,
alternative porous Ni foam with optimized pore
structure by facile method would be most enticing not
only for higher energy density for free-standing
advanced electrodes but also its low-cost application in
fields as energy storage, catalyst and sensors.
Glycine-nitrate combustion (GNC), a novel
illustration of sustainable redox reaction and propellant
chemistry, has proved to be a simple but cost-effective
method for scalable synthesis of porous and fine
advanced ceramics, catalysts and nanomaterials14, 15.
Typically, an oxidizer (O) and a fuel (F) are first mixed
in solution. When heated, the solution turns to vicious
gel and begins to foam after gelation. Then the redox
reaction initiates at critical ignition temperature (Tig)
and sustains due to intensive heat release. Meanwhile,
solid-state products are released, sintered into different
microstructure and made porous by the gaseous ones14-
17. Solution GNC received intensive attention when