Reverse electrodialysis (RED) using a bipolar membrane to suppress inorganic fouling around the cathode

Han, Ji-Hyung,Jeong, Namjo,Kim, Chan-Soo,Hwang, Kyo Sik,Kim, Hanki,Nam, Joo-Youn,Jwa, Eunjin,Yang, SeungCheol,Choi, Jiyeon Elsevier 2019 Water research Vol.166 No.-

<P><B>Abstract</B></P> <P>When operating reverse electrodialysis (RED) with several hundreds of cell pairs, a large stack voltage of more than 10 V facilitates water electrolysis, even when redox couples are employed for the electrode reaction. Upon feeding natural water containing multivalent ions, ion crossover through a shielding membrane causes inorganic scaling around the cathode and the interior of the membrane stack, due to the combination with the hydroxide ions produced via water reduction. In this work, we introduce a bipolar membrane (BPM) as a shielding membrane at the cathode to suppress inorganic precipitation. Water splitting in the bilayer structure of the BPM can block the ions diffusing from the catholyte and the feed solution, maintaining the current density. To evaluate the effect of the BPM on the inorganic precipitates, diluted sea salt solution is allowed to flow through the outermost feed channel near the cathode, in order to maintain as large a stack voltage as possible, which is important to induce water splitting in the BPM when incorporated into an RED stack of 100 cell pairs. We measure the electric power of the RED according to the arrangement of the BPM and compare it with that of conventional RED. The degree of inorganic scaling is also compared according to the kind of shielding membrane used (anion exchange membrane, cation exchange membrane, and BPM (Neosepta or Fumasep)). The BPM (Neosepta) shows the best performance for suppressing the formation of precipitates. It can hence be used to design a highly stable electrode system for long-term operation of a large-scale RED feeding natural water.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A bipolar membrane (BPM) as a shielding membrane at the cathode. </LI> <LI> A large stack voltage of RED facilitates water splitting in the BPM. </LI> <LI> A ∼5% reduction in <SUB> P d , m a x </SUB> was observed due to the overpotential for water splitting. </LI> <LI> Water splitting blocked the crossover of hydroxide ions and multivalent ions. </LI> <LI> BPM (Neosepta) showed much greater anti-inorganic fouling, compared to BPM (Fumasep). </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Promoting electrocatalytic overall water splitting with nanohybrid of transition metal nitride-oxynitride

Dutta, Soumen,Indra, Arindam,Feng, Yi,Han, HyukSu,Song, Taeseup Elsevier 2019 Applied Catalysis B Vol.241 No.-

<P><B>Abstract</B></P> <P>Excellent Electrochemical water splitting with remarkable durability can provide a solution for the increasing global energy demand. Herein, we report an efficient and stable overall water splitting system; cobalt nitride-vanadium oxynitride nanohybrid, prepared from the polyaniline (PANI) mediated synthetic protocol. This nanohybrid produces significantly higher water oxidation, proton reduction as well as overall water splitting performances compared to the cobalt nitride, vanadium oxynitride or even noble metal catalyst systems. Only 263 mV overpotential is required to reach 10 mA cm<SUP>−2</SUP> current density for oxygen evolution reaction (OER) and 118 mV for the same in case of hydrogen evolution reaction (HER). Finally, the bifunctional nanohybrid has been explored for the alkaline overall water splitting at cell voltage of 1.64 V to attain 10 mA cm<SUP>−2</SUP> current density with long term stability for 100 h. Post-catalytic analyses have revealed the formation of defect rich amorphous CoO<SUB>x</SUB> sites leading to high OER activity, whereas crystalline Co(OH)<SUB>2</SUB>-Co<I>δ</I> <SUP>+</SUP>-N (0 < <I>δ</I> < 2) centres are generated after HER. To the best of our knowledge, this is the first example of a nitride-oxynitride nanohybrid system employed for the overall water splitting, and its superior activity and durability recommend its potential for practical utilization.</P> <P><B>Highlights</B></P> <P> <UL> <LI> First report on metal nitride-oxynitride nanohybrid for water splitting. </LI> <LI> Fabrication of transition metal nitride without direct use of ammonia gas. </LI> <LI> Only 263 and 118 mV overpotential at 10 mA cm<SUP>−2</SUP> current density for OER and HER, respectively for the nanohybrid. </LI> <LI> Superior performance and stability than commercial RuO<SUB>2</SUB> and Pt-C couple in two-electrode alkaline water splitting reaction. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Hydrogen Production by Photoelectrochemical Water Splitting

H. W. Seo,J. S. Kim 한국진공학회(ASCT) 2018 Applied Science and Convergence Technology Vol.27 No.4

The basic principle and concept for hydrogen production via water-splitting process are introduced. In particular, recent research activities and their progress in the photoelectrochemical water-splitting process are investigated. The material perspectives of semiconducting photocatalysts are considered from metal oxides, including titanium oxides, to carbon compounds and perovskites. Various structural configurations, from conventional photoanodes with metal cathodes to tandem and nanostructures, are also studied. The pros and cons of each are described in terms of light absorption, charge separation/photoexcited electron-hole pair recombinations and further solar-to-hydrogen efficiency. In this research, we attempt to provide a broad view of up-to-date research and development as well as, possibly, future directions in the photoelectrochemical water-splitting field.

Bipolar membranes containing efficient and durable water splitting catalysts

송현비,문하늘,강문성 한국공업화학회 2020 한국공업화학회 연구논문 초록집 Vol.2020 No.-

In this study, we have developed a novel type of bipolar membranes (BPMs) for efficient water-splitting processes. BPMs were prepared via a pore-filling method and shown to possess excellent water-splitting efficiency and mechanical properties. In addition, efficient and durable metal complexes were examined as the catalysts for facilitating water-splitting in BPMs. Membrane characterizations and water-splitting experiments were also conducted to determine the optimum metal catalyst and loading amount. Consequently, it was confirmed that the BPM prepared under the optimum condition showed excellent stability as well as a better water-splitting flux than that of the commercial BPM. The detailed results will be presented at the conference. This work was supported by the National Research Foundation of Korea(NRF) grant funded by the Korea government(MSIT) (No. 2019R1A2C1089286).

Bifunctional NiFe inverse opal electrocatalysts with heterojunction Si solar cells for 9.54%-efficient unassisted solar water splitting

Song, Hakhyeon,Oh, Seungtaeg,Yoon, Hyun,Kim, Ka-Hyun,Ryu, Sangwoo,Oh, Jihun unknown 2017 Nano energy Vol.42 No.-

<P><B>Abstract</B></P> <P>Photovoltaic cell–electrolyzer combined systems have recently been considered a most promising route to commercialization of photoelectrochemical (PEC) water splitting although efficiency, stability, and cost remain major challenges. Herein, we develop a highly efficient and low-cost, bifunctional NiFe electrocatalyst that uses NiFe inverse opal nanostructures for both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). From their increased surface area, NiFe inverse opal structures can reduce the overpotential by ~ 70mV and ~ 90mV for OER and HER, respectively. In addition, correlations between increased surface area of inverse opal 3-dimensional nanostructures and electrocatalytic activity of OER and HER are explored. Furthermore, a NiFe inverse opal structure with an optimized number of thickness layers reduces the overpotential of water splitting by ~160mV. When integrated to four series-connected Si heterojunction (SHJ) solar cells, the NiFe inverse opal electrolyzer achieves a 9.54% solar-to-hydrogen conversion efficiency over 24h under a zero-bias condition. The combined PEC water splitting investigated in this work is expected to provide a basis for the design of highly efficient renewable and sustainable water electrolysis systems that incorporate earth-abundant, low-cost materials.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Ordered NiFe-mesostructures for bifunctional electrocatalysts for water splitting. </LI> <LI> The role of nano- and meso-structures for catalytic activity is suggested. </LI> <LI> Combination of NiFe inverse opals and Si heterojunction solar cells. </LI> <LI> 9.54% unassisted solar to hydrogen conversion efficiency is achieved for 25h. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Ni-Ferrite-Based Thermochemical Cycle for Solar Hydrogen Production

Hwang, Gab-Jin,Park, Chu-Sik,Lee, Sang-Ho,Seo, In-Tae,Kim, Jong-Won 한국공업화학회 2004 Journal of Industrial and Engineering Chemistry Vol.10 No.6

Ni-Ferrite (NiFe₂O₄) was prepared as a basic _metal oxide for a solar hydrogen production cycle consisting of a methane reduction step and a water-splitting step. All steps were performed at relatively low temperatures (below 1073 K). In the CH₄-reduction step, it was confirmed that CH₄ reduction of the prepared Ni-ferrite progressed through two reaction regions with an increase of reaction time. In one, CH₄ reacted with oxygen discharged from Ni-ferrite (region 1); in the other, the methane self-decomposition occurred (region 2). The water splitting step was performed using the reduced Ni-ferrite after the CH₄ reduction step in the two regions. In the water splitting step after the CH₄ reduction step (region 1), CO and CO₂gas were not detected. The maximum H₂ production rate was about 3.3 mL/min g-metal-oxide at 10 min. The H₂ production rate in the water splitting step after the CH₄ reduction step (region 2) was about 3.3 mL/min g-metal-oxide at any reaction time. We confirmed from the XRD patterns that the phase of the prepared Ni-bearing ferrites was changed in each reaction step and that the phase after the water splitting step returned to the phase before the methane reduction step.

Surface and bulk modification for advanced electrode design in photoelectrochemical water splitting

Haider, Zeeshan,Yim, Hee Won,Lee, Hae Won,Kim, Hyoung-il Elsevier 2020 International journal of hydrogen energy Vol.45 No.10

<P><B>Abstract</B></P> <P>Photoelectrochemical (PEC) water splitting provides a prominent strategy for harnessing solar energy in the production of sustainable hydrogen fuel from water. Over the past few decades, extensive efforts have been devoted to develop advanced electrodes for efficient PEC water splitting. This review presents the recent progress in the development of efficient photoanodes through two major approaches: surface modification, including co-catalyst-loading, passivation, and defect engineering; and bulk modification, including hybridization, dopant engineering, and structural control. By virtue of bulk and surface modification a considerable improvement in PEC activity has been obtained so far. Photocurrent response of various anodes observed in the range of 0.063 mA cm<SUP>−2</SUP> – 8.5 mA cm<SUP>−2</SUP> (as listed in Table 1) require further improvement to upgrade the overall performance efficiency of PEC cells.</P> <P>This review also provides a systematic overview of the fundamentals of PEC water splitting, as well as the key challenges and notable achievements made so far in terms of electrode design and material modification. Finally, future research perspectives that will further advance this field are discussed. The contribution of this paper is to provide fundamental information about bulk and surface modifications, which will aid in the design of advanced electrodes for high-performance PEC cells.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Recent progress on developing advanced photoanodes for PEC water-splitting. </LI> <LI> Bulk and surface modifications synergistically enhance PEC performance. </LI> <LI> Critical factors determining the efficiency of the PEC cell have been highlighted. </LI> <LI> Future challenges and perspectives for sustainable PEC water-splitting are discussed. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Tri-branched tri-anchoring organic dye for Visible light-responsive dye-sensitized photoelectrochemical water-splitting cells

박정현(Park, Jeong-Hyun),김재홍(Kim, Jae-Hong),안광순(Ahn, Kwang-Soon) 한국신재생에너지학회 2010 한국신재생에너지학회 학술대회논문집 Vol.2010 No.06

Photoelectrochemical (PEC) systems are promising methods of producing H2 gas using solar energy in an aqueous solution. The photoelectrochemical properties of numerous metal oxides have been studied. Among them, the PEC systems based on TiO2 have been extensively studied. However, the drawback of a PEC system with TiO2 is that only ultraviolet (UV) light can be absorbed because of its large band gap (3.2 - 3.4 eV). Two approaches have been introduced in order to use PEC cells in the visible light region. The first method includes doping impurities, such as nitrogen, into TiO2, and this technique has been extensively studied in an attempt to narrow the band gap. In comparison, research on the second method, which includes visible light water splitting in molecular photosystems, has been slow. Mallouk et al. recently developed electrochemical water-splitting cells using the Ru(II) complex as the visible light photosensitizer. the dye-sensitized PEC cell consisted of a dye-sensitized TiO2 layer, a Pt counter electrode, and an aqueous solution between them. Under a visible light (< 3 eV) illumination, only the dye molecule absorbed the light and became excited because TiO2 had the wide band gap. The light absorption of the dye was followed by the transfer of an electron from the excited state (S*) of the dye to the conduction band (CB) of TiO2 and its subsequent transfer to the transparent conducting oxide (TCO). The electrons moved through the wire to the Pt, where the water reduction (or H2 evolution) occurred. The oxidized dye molecules caused the water oxidation because their HOMO level was below the H2O/O2 level. Organic dyes have been developed as metal-free alternatives to the Ru(II) complexes because of their tunable optical and electronic properties and low-cost manufacturing. Recently, organic dye molecules containing multi-branched, multi-anchoring groups have received a great deal of interest. In this work, tri-branched tri-anchoring organic dyes (Dye 2) were designed and applied to visible light water-splitting cells based on dye-sensitized TiO2 electrodes. Dye 2 had a molecular structure containing one donor (D) and three acceptor (A) groups, and each ended with an anchoring functionality. In comparison, mono-anchoring dyes (Dye 1) were also synthesized. The PEC response of the Dye 2-sensitized TiO2 film was much better than the Dye 1-sensitized or unsensitized TiO2 films.

이미다졸륨 고분자 코팅을 통한 음이온교환막의 물분해 특성 제어

김도형,박진수,강문성,Kim, Do-Hyeong,Park, Jin-Soo,Kang, Moon-Sung 한국막학회 2015 멤브레인 Vol.25 No.2

In this study, novel pore-filled anion-exchange membranes (PFAEMs) with low electrical resistance, high permselectivity, and low water-splitting flux property under a concentration polarization condition have been developed for the enhancement in the efficiency of electrochemical water treatment processes. The base membranes have been prepared by filling a copolymer containing quaternary ammonium groups with an excellent ion-exchange capability into a porous polyolefin substrate, showing a high performance superior to that of a commercial membrane. In addition, it was confirmed that the electrochemical membrane performances are preserved while the water-splitting flux is effectively controlled by coating an imidazolium polymer onto the surface of the base membrane. The prepared PFAEMs revealed remarkably low electrical resistances of about 1/6~1/8 compared to those of a commercial membrane, and simultaneously low water-splitting flux comparable with that of cation-exchange membranes under a concentration polarization condition. 본 연구에서는 이온교환막을 이용한 전기화학적 수처리 공정의 효율을 향상시키기 위해 낮은 전기적 저항, 높은 이온선택 투과성, 및 농도분극 조건에서 낮은 물분해 플럭스 특성을 갖는 새로운 세공충진 음이온 교환막을 개발하였다. 다공성 폴리올레핀 기재에 이온교환능이 우수한 4급 암모늄기를 포함한 공중합 고분자를 충진하여 상용막 이상의 성능을 갖는 기저 멤브레인을 제조하였다. 또한 기저 막 표면에 이미다졸륨 고분자를 코팅하여 전기화학적 성능을 유지하며 동시에 물분해 플럭스를 효과적으로 제어할 수 있음을 확인하였다. 제조된 세공충진 음이온 교환막은 상용막 대비 약 1/6~1/8 수준의 매우 낮은 전기적 저항을 나타내었으며 동시에 농도분극 조건에서 양이온 교환막 수준의 낮은 물분해 플럭스를 나타내었다.

Well-designed Te/SnS₂/Ag artificial nanoleaves for enabling and enhancing visible-light driven overall splitting of pure water

Yan, Changzeng,Xue, Xiaolan,Zhang, Wenjun,Li, Xiaojie,Liu, Juan,Yang, Songyuan,Hu, Yi,Chen, Renpeng,Yan, Yaping,Zhu, Guoyin,Kang, Zhenhui,Kang, Dae Joon,Liu, Jie,Jin, Zhong unknown 2017 Nano energy Vol.39 No.-

<P><B>Abstract</B></P> <P>To produce hydrogen and oxygen from photocatalytic overall splitting of pure water provides a promising green route to directly convert solar energy to clean fuel. However, the design and fabrication of high-efficiency photocatalyst is challenging. Here we present that by connecting different nanostructures together in a rational fashion, components that cannot individually split water into H<SUB>2</SUB> and O<SUB>2</SUB> can work together as efficient photocatalyst with high solar-to-hydrogen (STH) energy conversion efficiency and avoid the use of any sacrificial reagent. Specifically, Te/SnS<SUB>2</SUB>/Ag artificial nanoleaves (ANLs) consist of ultrathin SnS<SUB>2</SUB> nanoplates grown on Te nanowires and decorated with numerous Ag nanoparticles. The appropriate band structure of Te/SnS<SUB>2</SUB> p-n junctions and the surface plasmon resonance of Ag nanoparticles synergistically enhance the quantum yield and separation efficiency of electron-hole pairs. As a result, Te/SnS<SUB>2</SUB>/Ag ANLs enable visible-light driven overall water-splitting without any sacrificial reagent and exhibit high H<SUB>2</SUB> and O<SUB>2</SUB> production rates of 332.4 and 166.2μmolh<SUP>−1</SUP>, respectively. Well-preserved structure after long-term measurement indicates its high stability. It represents a feasible approach for direct H<SUB>2</SUB> production from only sunlight, pure water, and rationally-designed ANL photocatalysts.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Te/SnS<SUB>2</SUB>/Ag ANLs heterostructure is prepared to catalyze overall water splitting. </LI> <LI> The catalyst show impressive H<SUB>2</SUB> and O<SUB>2</SUB> production rate under visible light. </LI> <LI> The structure and efficiency of catalyst shows no degradation after 10 days. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>