In this paper, we show the carbonization of binary composites consisting of graphene nanoplatelets and melamine (GNP/MM), multi-walled carbon nanotubes and melamine (CNT/MM) and trinary composites containing GNP, CNT, and MM. Additionally, the manuscript presents results on the influence of structural factors for the electrochemical performance of carbon composites on their catalytic activity. This study contributes to the wide search and design of novel hybrid carbon composites for electrochemical applications. We demonstrate that intensive nitrogen atom insertion is not the governing factor since hybrid system modifications and porous structure sometimes play a more crucial role in the tailoring of electrochemical properties of the carbon hybrids seen as a noble metal-free alternative to traditional electrode materials. Additionally, HRTEM and Raman spectra study allowed for the evaluation of the quality of the obtained hybrid materials.
Additive manufacturing transforms the landscape of modern microelectronics. Recent years have witnessed significant progress in the fabrication of 2D planar structures and free-standing 3D architectures. In this work, we present a much-needed intermediary approach: we introduce the Ultra-Precise Deposition (UPD) technology, a versatile platform for material deposition at micrometer scale on complex substrates. The versality of this approach is related to three aspects: material to be deposited (conductive or insulating), shape of the printed structures (lines, dots, arbitrary shapes), as well as type and shape of the substrate (rigid, flexible, hydrophilic, hydrophobic, substrates with pre-existing features). The process is based on the direct, maskless deposition of high-viscosity materials using narrow printing nozzles with the internal diameter in the range from 0.5 to 10 µm. For conductive structures we developed highly concentrated non-Newtonian pastes based on silver, copper, or gold nanoparticles. In this case, the feature size of the printed structures is in the range from 1 to 10 µm and their electrical conductivity is up to 40% of the bulk value, which is the record conductivity for metallic structures printed with spatial resolution below 10 µm. This result is the effect of the synergy between the printing process itself, formulation of the paste, and the proper sintering of the printed structures. We demonstrate a pathway to print such fine structures on complex substrates. We argue that this versatile and stable process paves the way for a widespread use of additive manufacturing for microfabrication.
This
work demonstrates the influence of high-quality protection
layers on Si–Cu2O micropillar arrays created by
pulsed laser deposition (PLD), with the goal to overcome photodegradation
and achieve long-term operation during photoelectrochemical (PEC)
water splitting. Sequentially, we assessed planar and micropillar
device designs with various design parameters and their influence
on PEC hydrogen evolution reaction. On the planar device substrates,
a Cu2O film thickness of 600 nm and a Cu2O/CuO
heterojunction layer with a 5:1 thickness ratio between Cu2O to CuO were found to be optimal. The planar Si/Cu2O/CuO
heterostructure showed a higher PV performance (Jsc = 20 mA/cm2) as compared to the planar Si/Cu2O device, but micropillar devices did not show this improvement.
Multifunctional overlayers of ZnO (25 nm) and TiO2 (100
nm) were employed by PLD on Si/Cu2O planar and micropillar
arrays to provide a hole-selective passivation layer that acts against
photocorrosion. A micropillar Si/ITO-Au/Cu2O/ZnO/TiO2/Pt stack was compared to a planar device. Under optimized
conditions, the Si/Cu2O photocathode with Pt as a HER catalyst
displayed a photocurrent of 7.5 mA cm–2 at 0 V vs
RHE and an onset potential of 0.85 V vs RHE, with a stable operation
for 75 h.
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