In this study, we undertook detailed experiments to increase hydrogen production efficiency by optimizing the thickness of titanium dioxide (TiO2) thin films. TiO2 films were deposited on p-type silicon (Si) wafers using atomic layer deposition (ALD) technology. The main goal was to identify the optimal thickness of TiO2 film that would maximize hydrogen production efficiency while maintaining stable operating conditions. The photoelectrochemical (PEC) properties of the TiO2 films of different thicknesses were evaluated using open circuit potential (OCP) and linear sweep voltammetry (LSV) analysis. These techniques play a pivotal role in evaluating the electrochemical behavior and photoactivity of semiconductor materials in PEC systems. Our results showed photovoltage tended to improve with increasing thickness of TiO2 deposition. However, this improvement was observed to plateau and eventually decline when the thickness exceeded 1.5 nm, showing a correlation between charge transfer efficiency and tunneling. On the other hand, LSV analysis showed bare Si had the greatest efficiency, and that the deposition of TiO2 caused a positive change in the formation of photovoltage, but was not optimal. We show that oxide tunneling-capable TiO2 film thicknesses of 1~2 nm have the potential to improve the efficiency of PEC hydrogen production systems. This study not only reveals the complex relationship between film thickness and PEC performance, but also enabled greater efficiency and set a benchmark for future research aimed at developing sustainable hydrogen production technologies.

Fluorine-doped tin oxide (FTO) has been used as a representative transparent conductive oxide (TCO) in various optoelectronic applications, including light emitting diodes, solar cells, photo-detectors, and electrochromic devices. The FTO plays an important role in providing electron transfer between active layers and external circuits while maintaining high transmittance in the devices. Herein, we report the effects of substrate rotation speed on the electrical and optical properties of FTO films during ultrasonic spray pyrolysis deposition (USPD). The substrate rotation speeds were adjusted to 2, 6, 10, and 14 rpm. As the substrate rotation speed increased from 2 to 14 rpm, the FTO films exhibited different film morphologies, including crystallite size, surface roughness, crystal texture, and film thickness. This FTO film engineering can be attributed to the variable nucleation and growth behaviors of FTO crystallites according to substrate rotation speeds during USPD. Among the FTO films with different substrate rotation speeds, the FTO film fabricated at 6 rpm showed the best optimized TCO characteristics when considering both electrical (sheet resistance of 13.73 Ω/□) and optical (average transmittance of 86.76 % at 400~700 nm) properties with a figure of merit (0.018 Ω-1).

광전기화학 성능을 향상시키기 위해 각 ZnO, ZnSe과 g-C3N4 소재의 장점을 살리도록 3성분계 적층 구조를 디자 인했다. 용액공정으로 FTO 기판위에서 ZnO 나노로드 어레이가 성장하도록 한 후 ZnO표면에 Se을 부착시켜 ZnO표면에 서 ZnSe층이 형성 되도록 이온 치환법을 도입하였다. ZnO/ZnSe 나노로드 위에 g-C3N4 층을 스핀코팅 한 후 각 층이 화 학적 접합이 되도록 질소 분위기 하에서 열처리를 하였다. AM 1.5G, 0.5 V 외부전압하에서 각 적층구조별로 광전기화학 적 전류밀도를 측정하였고 비교 결과 ZnO/ZnSe/g-C3N4 나노로드가 ZnO 및 ZnO/ZnSe 나노로드에 비하여 보다 높은 광 전류 밀도가 측정되었다. 수직 정렬된 ZnO 육각 프리즘형태는 큰 비표면적과 축 방향을 따라 전자 흐름을 원활히 하고, ZnSe 층은 비표면적과 광흡수 범위를 더욱 넗히는 효과를 가져왔다. 이로 인하여 ZnO/ZnSe/g-C3N4 삼원 접합 전극의 향상된 성능은 가시광선 흡수범위 확장, 전하 분리 강화 및 전자 전도도 향상으로 인한 시너지 효과에 기인되는 것으로 판단된다.

Chlor-alkali (CA) membranes as key materials to generate chlorine gas and sodium hydroxide are composed of sulfonic acid layer (S-layer) and carboxylic acid layer (C-layer) to provide fast sodium ion transport and slow hydroxide ion diffusion, respectively. Aciplex F, a representative CA membrane is made in a double layer form via thermal adhesion of both layers after each single layer film is independently fabricated. Unfortunately, the membrane fabrication induces delamination particularly in their interface as a result of hydroxide ion diffusion occurring during CA operation, leading to rapid increase in electrochemical overpotential. In this study, selective chemical conversion technique was developed to solve the delamination issue. Their effectiveness was proved by applying the same concept to a wide range of PFSA membrane.

Saline water electrolysis is an electrochemical process to produce valued chemicals by applying electric power. Perfluorinated sulfonic acid (PFSA) ionomers have been used as polymer electrolyte membrane (PEM) materials owing to their high sodium ion selectivity and barrier properties. However, sulfonic acid groups in PFSA ionomers are chemically decomposed under a basic catholyte condition, which makes the PEM materials lose their ionic selectivity and Faraday efficiency. In this study, double layered membranes were prepared by anchoring cross-linked hydrocarbon ionomers, as a protection layer to catholyte atmosphere, into the water channels, particularly, located at around the surface of a PFSA membrane. Here, each monomer results in the identical chemical architecture and different free volume content when polymerized.

본 연구에서는 전기분해 방법을 이용한 질산성질소(NO3 --N) 분해가 TiO2 nanotube plate 및 구리, 니켈, 스테인리스 스틸, 알루미늄, 주석, 티타늄을 환원전극으로 사용하였을 때 가능한지를 평가하였다. 전극의 전기화학적 특성 평가는 임피던스 측정을 하여 비교하였고, TiO2 nanotube plate의 표면 분석은 주사전자현미경을 통해 SEM 및 BET 분석법을 이용한 비표면적 분석을 통해 비교하였다. 질산성질소 전해실험의 경우 90분의 실험을 진행하였으며, 실험 결과 전극 표면의 부식이 수반되지 않은 TiO2 nanotube plate가 기타 금속 전극에 비해 질산성질소 환원 반응속도가 가장 뛰어난 것으로 확인되었다.

Chlor-alkali (CA) membrane process is a commercially useful process to produce valued chemicals such as chlorine, sodium hydroxide and hydrogen via salined water electrolysis using sodium ion (Na+)-selective membranes. The most important issue in CA process is to reduce high energy consumption. A plausible solution is to obtain highly Na+-conductive membranes. The representative membrane materials are chemically stable perfluorinated sulfonic acid (PFSA) ionomers such as Nafion® and Aciplex®. PFSA membranes, but it is necessary to develop alternatives to PFSA membranes. In this study, a sulfonated poly(arylene ether sulfone) copolymer membrane is radiation-grafted with a highly sulfonated poly(styrene) used as a side chain material.

Saline water electrolysis is a representative electrochemical conversion to produce chlorine gas and sodium hydroxide as major products by applying electric power. Perfluorinated sulfonic acid (PFSA) ionomers have been usually used as polymer electrolyte membrane materials owing to high sodium ion selectivity and strong resistance to acidic compounds (e.g., Cl2, HCl and so on) produced in anode. However, PFSA ionomers have been suffering from chemical degradation occurring when exposed under harsh basic condition in cathode. In this study, double layered chlor-alkali membranes were prepared by anchoring crosslinked hydrocarbon ionomer via radical polymerization technique in water channels located in a surface layer of PFSA ionomer membranes and electrochemically evaluated.

이산화탄소 전환 기술은 이산화탄소를 원료로 유용한 화합물을 생산하는 기술로서 지속적인 탄소원의 활용 및 고부가 가치의 화합물 생산을 통한 이익 창출이 가능하다. 다양한 이산화탄소 전환 기술 중에서도 전기 에너지를 이용한 이산화탄소 전환 기술은 유용 화합물 생산 외에도 신재생에너지 저장 기술로 활용할 수 있어서 최근 그 중요성이 부각되고 있다. 그러나 열역학적으로 안정한 이산화탄소의 환원 반응은 많은 에너지를 필요로 하므로 기술의 경제성 확보 및 실질적인 탄소 중립을 구현하기 위해서는 생성물에 대한 높은 선택성을 가지는 촉매 개발 및 효율적인 반응 시스템 개발이 필수적이다. 본 연구에서는 고분자 전해질 막을 이용하여 전기화학적 이산화탄소 전환을 통해 개미산염을 제조하였다.

수소는 산업용 전력생산, 자동차용 연료 등을 위한 대체가능한 에너지 담체로 인식되고 있다. 미래 저탄소 에너지 시스템에서 에너지 저장은 전력 수요에 유연하지 않거나 간헐적인 공급의 균형을 이루기 위한 중추적인 역할을 담당할 수 있 을 것이다. 수소는 에너지 담체로서 전기에너지를 화학에너지로, 화학에너지를 전기에너지로 변환할 수 있는 에너지 저장 방 법 중의 하나이다. 수소제조 방법 중에서, 특히, 물의 전기분해를 이용한 방법은 신재생 에너지원과의 접목을 고려할 때 가장 효율적이고 실용적인 방법으로 여겨지고 있다. 물 전기분해 수소제조 기술은 전기를 이용하여 수소를 물로부터 직접 제조하 는 방법으로, 화석연료 이용 제조방법과 비교하여 수소를 제조할 때 지구환경 오염물질인 이산화탄소의 배출이 없다. 수소제 조 방법 중의 하나인 물 전기분해의 원리와 물 전기분해의 종류인 알칼리 수전해(AWE, alkaline water electrolysis), 고분자 전해질막 수전해(PEMWE, polymer electrolyte membrane water electrolysis), 고온 수증기 전기분해(HTSE, high temperature steam electrolysis)에 대하여 분석하고자 하였다. 물 전기분해는 수소제조 방법의 하나로 연구가 진행되고 있으며, 최근에는 PTG (power to gas)와 PTL (power to liquid) 시스템의 요소기술로도 주목을 받고 있다. 본 총설에서는 물 전기분해에 대한 원리와 종류, 특히 알칼리 수전해에 대한 최근 연구동향에 대해 설명하였다.

이온교환막은 수용액중의 양이온 및 음이온을 선택적으로 분리할 수 있는 이온선택성 막으로서 기본적 개념, 실직적 응용 분야, 기술적 적절성 등에 있어서 다양한 공정들에 폭넓게 사용되어지고 있다. 이온교환막을 응용한 공정은 최근 저가·고효율 이온교환막의 개발로 경제적이며 친환경적인 분리 공정으로 주목받고 있다. 이온교환막을 이용한 분리 공정은 초순수 제조, 이온성 물질의 분리·정제, 산·염기 제조와 같은 다양한 산업 분야에 적용이 가능하다. 본 발표에서는 이온교환막의 상업적 공정 적용 사례를 소개하고 향후 이온교환막의 개선방향에 대한 제안을 통해 보다 실용적인 국내 이온교환막의 개발에 도움이 되고자 한다.

염수전기분해(saline water electrolysis) 또는 클로로-알칼리 막공정(chlor-alkali membrane process)은 양이온교환 막과 전극으로 구성되는 전해셀에 전기를 가하여, 고순도(> 99%)의 고부가가치 화합물(예 : 염소, 수소, 수산화나트륨)을 직 접 제조하는 화학공정이다. 염수전기분해의 경제성은 동일한 양의 화합물을 생산하기 위해 투여되는 에너지 소비량을 저감 시킴으로 달성될 수 있다. 이러한 이슈는 전해질이나 전극의 고유 저항을 줄이거나, 전해질과 전극 사이의 계면 저항을 감소 시킴으로 달성시킬 수 있다. 본 연구에서는 전자빔 동시조사법을 사용하여, 높은 화학적 안정성을 지닌 탄화수소계 술폰산 이 오노머 막의 표면에 높은 이온선택성을 갖는 고분자를 접목 시키는 시도가 이루어졌다. 이를 통해, 고분자 전해질 막의 이온 전도성을 보완함과 동시에, 전극과의 계면 저항을 감소시켜, 전기화학적 효율 향상이 이루어짐을 관찰하였다.

We report on the fabrication and characterization of a novel Cu2O/CuO heterojunction structure with CuO nanorods embedded in Cu2O thin film as an efficient photocathode for photoelectrochemical (PEC) solar water splitting. A CuO nanorod array was first prepared on an indium-tin-oxide-coated glass substrate via a seed-mediated hydrothermal synthesis method; then, a Cu2O thin film was electrodeposited onto the CuO nanorod array to form an oxide semiconductor heterostructure. The crystalline phases and morphologies of the heterojunction materials were examined using X-ray diffraction and scanning electron microscopy, as well as Raman scattering. The PEC properties of the fabricated Cu2O/CuO heterojunction photocathode were evaluated by photocurrent conversion efficiency measurements under white light illumination. From the observed PEC current density versus voltage (J-V) behavior, the Cu2O/CuO photocathode was found to exhibit negligible dark current and high photocurrent density, e.g. −1.05 mA/cm2 at −0.6 V vs. Hg/HgCl2 in 1 mM Na2SO4 electrolyte, revealing the effective operation of the oxide heterostructure. The photocurrent conversion efficiency of the Cu2O/CuO photocathode was estimated to be 1.27% at −0.6 V vs. Hg/HgCl2. Moreover, the PEC current density versus time (J-T) profile measured at −0.5 V vs. Hg/HgCl2 on the Cu2O/CuO photocathode indicated a 3-fold increase in the photocurrent density compared to that of a simple Cu2O thin film photocathode. The improved PEC performance was attributed to a certain synergistic effect of the bilayer heterostructure on the light absorption and electron-hole recombination processes.

Ionomers are polymeric materials containing fixed charged ions (e.g., – SO3 -) to transport their counter ions (e.g., H+, Li+, Na+ and so on) selectively and have been widely used as key components for membrane and unit cell formation targeted for renewable energy generation (e.g., polymer electrolyte membrane fuel cells(PEMFC), redox flow batteries, and reverse electrodialyses) and valued chemical production (e.g., water and brine electrolysis). There are advantages such as high processability, easy solvent evaporation, and chemical inertness, when the ionomers are in the dissolved or dispersed states in water-alcohol mixtures to be applied for these applications. Unfortunately, it is difficult to make homogeneous solution or dispersion using the ionomers with hydrophilic levels undissolved in water. In this study, water-alcohol nanodipsersion with perfluorinated or hydrocarbon sulfonic acid ionomers are fabricated and their feasibilities as PEMFC and electrolysis materials are evaluated.

Fluorine-doped tin oxide (FTO) nanoparticles have been successfully synthesized using ultrasonic spray pyrolysis. The morphologies, crystal structures, chemical bonding states, and electrochemical properties of the nanoparticles are investigated. The FTO nanoparticles show uniform morphology and size distribution in the range of 6-10 nm. The FTO nanoparticles exhibit excellent electrochemical performance with high discharge specific capacity and good cycling stability (620mA h g−1 capacity retention up to 50 cycles), as well as excellent high-rate performance (250 mA h g−1 at 700mAg−1) compared to that of commercial SnO2. The improved electrochemical performance can be explained by two main effects. First, the excellent cycling stability with high discharge capacity is attributed to the nano-sized FTO particles, which are related to the increased electrochemical active area between the electrode and electrolyte. Second, the superb high-rate performance and the excellent cycling stability are ascribed to the increased electrical conductivity, which results from the introduction of fluorine doping in SnO2. This noble electrode structure can provide powerful potential anode materials for high-performance lithiumion batteries.

Hydrogen is considered a potential future energy source. Among other applications of hydrogen, hydrogen-rich water is emerging as a new health care product in industrial areas. Water electrolysis is typically used to generate a hydrogen rich water system. We annealed 10AA carbon paper in air to use it as an electrode of a hydrogen rich water generator. Driven by annealing, structural changes of the carbon paper were identified by secondary electron microscope analysis. Depending on the various annealing temperatures, changes of the hydrophilic characteristics were demonstrated. The crystal structures of pristine and heat-treated carbon paper were characterized by X-ray diffraction. Improvement of the efficiency of the electrochemical oxygen evolution reaction was measured via linear voltammetry. The optimized annealing temperature of 10AA carbon paper showed the possibility of using this material as an effective hydrogen rich water generator.