Wednesday, November 18, 2015

Graphene - ALD bendable Supercaps by Nanyang Technological University and Partners

Nanowerk had an interesting post today on how Nanyang Technological University and Partners in Singapore and China are using graphene and ALD Metal Nitrides to fabricate bendable solid-state asymmetric super capacitors. Check out the processing to achieve the metal nitrides below - not the usual way but via the oxides and solution based chemistry! I assume that graphene is a tricky material to grow metal nitrides on


Illustration of the asymmetric supercapacitor, consisting of vertically aligned graphene nanosheets coated with iron nitride and titanium nitride as the anode and cathode, respectively. (as published in Nanowerk, ©WILEY-VCH Verlag)


"To get the maximum benefit from the graphene surface, the team used a precise method for creating thin-films, a process known as atomic layer deposition, to grow two different materials on vertically aligned graphene nanosheets: titanium nitride for their supercapacitor’s cathode and iron nitride for the anode." 



Tracking back to the original publication in Advanced Materials "All Metal Nitrides Solid-State Asymmetric Supercapacitors" DOI: 10.1002/adma.201501838 there are some more details available in the free to download supporting information from the authors where it is reviled that a BENEQ TFS 200 ALD reactor was used for the cathode and anode. Here´s the link and some details are given below:

A BENEQ TFS 200 that come in many sorts and flavours (www.beneq.com)

Electrode Material Synthesis

Preparation of TiN@GNS Cathode: All chemicals were bought from Sigma Aldrich and used without further purification. Graphene nanosheets (467 m2 g-1) were provided by INCUBATION ALLIANCE, INC. The cathode fabrication process is mainly composed of two steps: TiO2 deposition by atomic layer deposition (ALD) and transferring to nitride through annealing in ammonia (NH3) atmosphere. Before ALD, the GNS substrates were treated with oxygen plasma at 200 W for 10 minutes with an O2 gas flow of 100 sccm, 70 mTorr. In a typical ALD (Beneq TFS 200) process, 120 °C was applied to the GNS substrate with TiCl4 and water as the titanium and oxygen source, respectively. 166 cycles (~ 1.2 Å per cycle) deposition was conducted to obtain 20 nm TiO2 coating during which the reaction chamber was maintained with a steady N2 steam at 300 sccm (cubic centimeter per minute) at 1.0 mbar. The sample of TiO2@GNS was then annealed in NH3 atmosphere at 800 °C for 1 h with a gas flow of 50 sccm and heating rate of 20 °C per minute. The control sample of TiO2@GNS was synthesized with the same ALD process. 

Preparation of Fe2N@GNS Anode: 20 nm ZnO was deposited on GNS (oxygen plasma pretreated) with ALD at 200 °C. The ZnO@GNS sample was then immersed in 0.5 M Fe(NO3)3 solution for 2 h to have a thorough transformation from ZnO to FeOOH as reported by the previous work[1]. The FeOOH@GNS sample was then annealed with the same NH3 atmosphere situation at a lower temperature of 600 °C. The control sample of FeOOH@GNS was fabricated by the same method just without the afterward annealing.

Also Available in the supporting information linked above is a quite impressive results from a bending test odf a charged super capacitor (see figure below)


Capacitance retention of the full device at different bending conditions. "All Metal Nitrides Solid-State Asymmetric Supercapacitors" DOI: 10.1002/adma.201501838 (©WILEY-VCH Verlag).