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[Figure1] Researcher Young-Been Kim 

AMSE Young-Been Kim under the Ph.D. program in Prof. Hyung Koun Cho‘s research team fabricated a high-efficient solar energy water splitting system that operates in alternating current (AC) voltage.

By designing an electrochemical deposition-based precursor synthesis process in order to micro-control based on thermodynamic morphology of Cu-In-Se (CIS), the research team developed a semiconductor structure where secondary phases coexist through the selenization process. Based on that, the team built the pulse-driven system in which enables high hydrogen evolution.

The multiphasic structure has improved the charge transport efficiency due to the expansion of the depletion region formed inside and on the surface of semiconductor electrodes. It can also generate photocurrent at reduction under negative (-) voltage and oxidation under positive (+) voltage due to the presence of multiphase. Consequently, the pulse-driven system is the new mechanism that can fully leverage the entire photocurrent generated out of AC output. 

Pulse-driven photoelectrochemical (PEC) water splitting has been introduced to improve Hydrogen evolution efficiency by destroying the charge accumulation and electrical double layer (ionic layer) of the electrode surface causing the loss. Herein, the research team demonstrated first significant performance in the field of photoelectrochemical water-splitting employing semiconductor electrodes. Furthermore, efficient hydrogen evolution was confirmed by suppressing the formation of large-size cluster bubbles and facilitating hydrogen ion adsorption. Specifically, Through a 156% improvement in hydrogen evolution over the DC voltage system, Researcher Kim attested the superior performance of pulse-driven PEC water splitting system.

Along with public attention on hydrogen energy in which shows high efficiency as renewable energy to replace petroleum, water-splitting research using light to generate hydrogen is increasingly being active. Thus, research has been conducted on photoactive materials that can generate high current under sunlight. However, it was limited to single conductivity types in which shows very low efficiency of photo-generated charge transport due to the neutrality of the inner area of absorbers.

Consequently, the researchers, by focusing on the development of multi-phase chalcogenide materials that enhance charge transport efficiency, enabled utilizing both photocathode and photoanode by controlling the precursor synthesis and selenization process.

This research was supported by Samsung Research Funding &Incubation Center of Samsung Electronics [grant number SRFC-MA170206].

The paper was published online in January 2021 in Applied Catalogis B: Environmental (IF 16.683), a SCI journal within the top 1.94% in materials and environmental engineering category.

 

[Figure 2] The photo-generated minority carriers effectively flow into interleaved depletion regions and transport along the externally induced built-in field at 0 V vs RHE.

[Figure 3] (a) Sequential steps illustrating one-cycle of current behavior in chronoamperometry result under pulse bias of 0 and 0.8 V vs RHE under light illumination (b) schematic diagrams for charge transport mechanism under constant light illumination from p-n interleaved CIS photoelectrode, where (Steps 1 and 3 ) the high-density charge transport through interleaved depletion regions; and (Steps 2 and 4 ) charge accumulation at the surface region and equilibrium state indicating a saturated steady state. (c) CA results and hydrogen evolution rate of the CIS/AZO/TiO2/Pt photoelectrode at pulse bias of 0 and 0.8 V vs RHE with alternating frequency of 150 cpm (1 M Na2SO4 electrolyte buffered at pH 5 with potassium borate solution) under constant 1 sun light illumination.

[Figure 4] (a) Electrical double layer (EDL) formation under negative biased electrode (b) Hydrogen generation mechanisms through the reduction reaction in the electrolyte (c) Active area loss due to gas agglomeration produced when DC power has driven