The Journal of
the Korean Journal of Metals and Materials

The Journal of
the Korean Journal of Metals and Materials

Monthly
  • pISSN : 1738-8228
  • eISSN : 2288-8241

Editorial Office


  1. ์ถฉ๋ถ๋Œ€ํ•™๊ต ๋„์‹œ ยท ์—๋„ˆ์ง€ ยท ํ™˜๊ฒฝ ์œตํ•ฉ ํ•™๋ถ€ (1Department of Urban, Energy, and Environmental Engineering, Chungbuk National University, Chungdae-ro 1, Seowon-Gu, Cheongju, Chungbuk, 28644 Republic of Korea)
  2. ๋ถ€์‚ฐ๋Œ€ํ•™๊ต ์žฌ๋ฃŒ๊ณตํ•™๊ณผ (2Department of Materials Science and Engineering, Pusan National University, Busan, 46241, Republic of Korea)
  3. ๋‚˜๋…ธ์œตํ•ฉ๋ฐ˜๋„์ฒด๊ณตํ•™๋ถ€ ๋‚˜๋…ธ์œตํ•ฉ๊ณตํ•™์ „๊ณต (3Department of Nanotechnology Engineering, Pukyong National University, Busan, 48547 Korea)
  4. ๋‹จ๊ตญ๋Œ€ํ•™๊ต ์‹ ์†Œ์žฌ๊ณตํ•™๊ณผ (4Department of Materials Science and Engineering, Dankook University, Cheonan, Chungnam 31116, Republic of Korea)
  5. ํ•œ๊ตญ์žฌ๋ฃŒ์—ฐ๊ตฌ์› ์—๋„ˆ์ง€ํ™˜๊ฒฝ์žฌ๋ฃŒ์—ฐ๊ตฌ๋ณธ๋ถ€ ์ˆ˜์†Œโ€ง์ „์ง€์žฌ๋ฃŒ์—ฐ๊ตฌ์„ผํ„ฐ (5Department of Hydrogen Energy Materials, Surface & Nano Materials Division, Korea Institute of Materials Science (KIMS), Changwon, 51508 Republic of Korea)
  6. ๋ถ€๊ฒฝ๋Œ€ํ•™๊ต ๋‚˜๋…ธ์œตํ•ฉ๋ฐ˜๋„์ฒด๊ณตํ•™๋ถ€ ์ฐจ์„ธ๋Œ€๋ฐ˜๋„์ฒด์ „๊ณต (6Division of Nanotechnology and Semiconductor Engineering, Pukyong National University, 45 Yongso-Ro, Busan, 48513, Republic of Korea)
  7. ๋ถ€์‚ฐ๋Œ€ํ•™๊ต ๋‚˜๋…ธ์—๋„ˆ์ง€๊ณตํ•™๊ณผ (7Department of Nanoenergy Engineering, Pusan National University, Busandaehak-ro 63 beon-gil 2, Geumjeong-gu, Busan 46241, Republic of Korea)
  8. ๋ถ€์‚ฐ๋Œ€ํ•™๊ต ๋‚˜๋…ธ์œตํ•ฉ๊ธฐ์ˆ ํ•™๊ณผ (8Department of Nano Fusion Technology, Pusan National University, Busandaehak-ro 63 beon-gil 2, Geumjeong-gu, Busan 46241, Republic of Korea)



Supercapacitor, Pseudocapacitor, MOF, Metal support template, Energy storage

1. ์„œ ๋ก 

์ „ ์„ธ๊ณ„ ์—๋„ˆ์ง€ ์ˆ˜์š”์˜ ์ง€์†์ ์ธ ์ฆ๊ฐ€์™€ ํ™”์„์—ฐ๋ฃŒ ์‚ฌ์šฉ์— ๋”ฐ๋ฅธ ์˜จ์‹ค๊ฐ€์Šค ๋ฐฐ์ถœ ํ™•๋Œ€๋Š” ์ง€์† ๊ฐ€๋Šฅํ•œ ์—๋„ˆ์ง€๋กœ์˜ ์ „ํ™˜ ํ•„์š”์„ฑ์„ ๋”์šฑ ๋ถ€๊ฐ์‹œํ‚ค๊ณ  ์žˆ๋‹ค[1-3]. ํŠนํžˆ ํƒœ์–‘๊ด‘ ๋ฐ ํ’๋ ฅ๊ณผ ๊ฐ™์€ ์žฌ์ƒ์—๋„ˆ์ง€์›์€ ์ฒญ์ •ํ•˜๊ณ  ์ž ์žฌ์ ์œผ๋กœ ๋ฌดํ•œํ•˜์ง€๋งŒ, ๊ธฐ์ƒ ์กฐ๊ฑด์— ๋”ฐ๋ฅธ ์ถœ๋ ฅ ๋ณ€๋™์„ฑ์ด๋ผ๋Š” ๊ฐ„ํ—์„ฑ ๋ฌธ์ œ๋ฅผ ์ง€๋‹Œ๋‹ค[4]. ์ด๋Ÿฌํ•œ ๋ณ€๋™์„ฑ์€ ์ „๋ ฅ๋ง ์•ˆ์ •์„ฑ์„ ์ €ํ•ดํ•  ์ˆ˜ ์žˆ์œผ๋ฏ€๋กœ, ์ด๋ฅผ ์™„ํ™”ํ•˜๊ธฐ ์œ„ํ•œ ๊ณ ์„ฑ๋Šฅ ์—๋„ˆ์ง€ ์ €์žฅ ์žฅ์น˜ ๊ฐœ๋ฐœ์ด ํ•„์ˆ˜์ ์ด๋‹ค[5].

๊ธฐ์กด ์ด์ฐจ์ „์ง€ ๋ฐ ์ˆ˜์†Œ ๊ธฐ๋ฐ˜ ์—๋„ˆ์ง€ ์ €์žฅ ์‹œ์Šคํ…œ์€ ์žฅ๊ธฐ ์—๋„ˆ์ง€ ์ €์žฅ์—๋Š” ์ ํ•ฉํ•˜๋‚˜, ์žฌ์ƒ์—๋„ˆ์ง€์˜ ๊ฐ„ํ—์„ฑ ๋Œ€์‘์— ์š”๊ตฌ๋˜๋Š” ์‹ ์†ํ•œ ์ถœ๋ ฅ ์‘๋‹ต์„ฑ ์ธก๋ฉด์—์„œ๋Š” ํ•œ๊ณ„๋ฅผ ๋ณด์ธ๋‹ค[6]. ๋ฐ˜๋ฉด, ์Šˆํผ์ปคํŒจ์‹œํ„ฐ๋Š” ๋†’์€ ์ถœ๋ ฅ ๋ฐ€๋„, ์ดˆ๊ณ ์† ์ถฉยท๋ฐฉ์ „ ํŠน์„ฑ, ๊ทธ๋ฆฌ๊ณ  ์ˆ˜์‹ญ๋งŒ ํšŒ ์ด์ƒ ์œ ์ง€๋˜๋Š” ์žฅ๊ธฐ ์‚ฌ์ดํด ์•ˆ์ •์„ฑ์„ ๋™์‹œ์— ์ œ๊ณตํ•˜์—ฌ ์žฌ์ƒ์—๋„ˆ์ง€์˜ ๋‹จ๊ธฐ ๋ณ€๋™์„ ํšจ๊ณผ์ ์œผ๋กœ ์™„์ถฉํ•  ์ˆ˜ ์žˆ๋‹ค[7,8]. ์ด๋Ÿฌํ•œ ํŠน์„ฑ์œผ๋กœ ์ธํ•ด ์Šˆํผ์ปคํŒจ์‹œํ„ฐ๋Š” ์ „๋ ฅ๋ง ์•ˆ์ •ํ™”๋ฟ ์•„๋‹ˆ๋ผ ์ „๊ธฐ์ฐจ ํšŒ์ƒ์ œ๋™ ์‹œ์Šคํ…œ, ๋ฌด์ •์ „ ์ „์›์žฅ์น˜(UPS) ๋“ฑ ๋‹ค์–‘ํ•œ ์‘์šฉ ๋ถ„์•ผ์—์„œ ํ•ต์‹ฌ์ ์ธ ์ฐจ์„ธ๋Œ€ ์—๋„ˆ์ง€ ์ €์žฅ ๊ธฐ์ˆ ๋กœ ์ž๋ฆฌ๋งค๊น€ํ•˜๊ณ  ์žˆ๋‹ค[9,10]. ์Šˆํผ์ปคํŒจ์‹œํ„ฐ๋Š” ์ „์ง€์™€ ์ผ๋ฐ˜ ์ปคํŒจ์‹œํ„ฐ์˜ ์ค‘๊ฐ„์  ํŠน์„ฑ์„ ๊ฐ€์ง„ ์—๋„ˆ์ง€ ์ €์žฅ ์žฅ์น˜๋กœ, ์ „์ง€์™€ ์œ ์‚ฌํ•˜๊ฒŒ ์ „๊ทน ํ‘œ๋ฉด์—์„œ ์‚ฐํ™”ยทํ™˜์› ๋ฐ˜์‘์„ ํ†ตํ•œ ์ค€์ „๊ธฐํ™”ํ•™์  ์ „ํ•˜ ์ €์žฅ(pseudocapacitance)์ด ๊ฐ€๋Šฅํ•˜๋ฉฐ, ๋™์‹œ์— ์ „๊ทนโ€“์ „ํ•ด์งˆ ๊ณ„๋ฉด์—์„œ ์ „๊ธฐ์ด์ค‘์ธต(electric double layer capacitance, EDLC)์„ ํ˜•์„ฑํ•˜์—ฌ ๋ฌผ๋ฆฌ์ ์œผ๋กœ ์ „ํ•˜๋ฅผ ์ €์žฅํ•œ๋‹ค[11]. ํŠนํžˆ, Faraday ๋ฐ˜์‘ ๊ธฐ๋ฐ˜์˜ pseudocapacitor๋Š” ๋‹จ์œ„ ๋ฉด์ ๋‹น ์ „ํ•˜ ์ €์žฅ ์šฉ๋Ÿ‰์ด ์ปค์„œ EDLC๋ณด๋‹ค ๋†’์€ ์—๋„ˆ์ง€ ๋ฐ€๋„๋ฅผ ๊ตฌํ˜„ํ•  ์ˆ˜ ์žˆ๋‹ค[12]. ๋”ฐ๋ผ์„œ ๊ณ ์„ฑ๋Šฅ ์Šˆํผ์ปคํŒจ์‹œํ„ฐ ๊ฐœ๋ฐœ์—์„œ๋Š” pseudocapacitor ํŠน์„ฑ ํ–ฅ์ƒ์ด ํ•ต์‹ฌ ์—ฐ๊ตฌ ๊ณผ์ œ๋กœ ์—ฌ๊ฒจ์ง„๋‹ค. ์ด๋Ÿฌํ•œ ํŠน์„ฑ์„ ํ–ฅ์ƒ์‹œํ‚ค๊ธฐ ์œ„ํ•œ ์ „๋žต ์ค‘ ํ•˜๋‚˜๋กœ, ์ „๊ทน ์†Œ์žฌ์˜ ๊ตฌ์กฐ์ ยทํ™”ํ•™์  ์„ฑ๋Šฅ์„ ๊ฐœ์„ ํ•˜๋Š” ๋ฐฉ๋ฒ•์ด ํšจ๊ณผ์ ์ด๋ฉฐ, ์šฐ์ˆ˜ํ•œ ์ „๊ทน ์†Œ์žฌ ๊ฐœ๋ฐœ์€ pseudocapacitor ์„ฑ๋Šฅ ๊ทน๋Œ€ํ™”์˜ ํ•ต์‹ฌ ์ ‘๊ทผ๋ฒ•์œผ๋กœ ํ‰๊ฐ€๋œ๋‹ค[12].

๊ธˆ์†โ€“์œ ๊ธฐ ๊ณจ๊ฒฉ์ฒด(Metalโ€“Organic Framework, MOF)๋Š” ๊ธˆ์† ์ด์˜จ ๋˜๋Š” ๊ธˆ์† ํด๋Ÿฌ์Šคํ„ฐ์™€ ์œ ๊ธฐ ์—ฐ๊ฒฐ์ฒด(organic linker)๊ฐ€ ๊ฒฐํ•ฉํ•˜์—ฌ ํ˜•์„ฑ๋œ 3์ฐจ์› ์œ ยท๋ฌด๊ธฐ ํ•˜์ด๋ธŒ๋ฆฌ๋“œ ๊ตฌ์กฐ์ฒด๋กœ, ๊ทœ์น™์ ์ธ ๋‹ค๊ณต์„ฑ ๊ตฌ์กฐ์™€ ๋„“์€ ๋น„ํ‘œ๋ฉด์ ์„ ํ†ตํ•ด ๋†’์€ ํ™œ์„ฑ ํ‘œ๋ฉด์„ ์ œ๊ณตํ•œ๋‹ค[13,14]. ์ด๋Ÿฌํ•œ ํŠน์„ฑ์œผ๋กœ MOF๋Š” ๊ฐ€์Šค ์ €์žฅยท๋ถ„๋ฆฌ, ์ด‰๋งค, ์„ผ์„œ, ์—๋„ˆ์ง€ ์ €์žฅ ์žฅ์น˜ ๋“ฑ ๋‹ค์–‘ํ•œ ๋ถ„์•ผ์—์„œ ํ™œ์šฉ๋˜๊ณ  ์žˆ์œผ๋ฉฐ, ํŠนํžˆ ์Šˆํผ์ปคํŒจ์‹œํ„ฐ ์ „๊ทน ์†Œ์žฌ๋กœ ํ™œ์šฉ๋  ๊ฒฝ์šฐ ์ „ํ•˜ ์ €์žฅ ํšจ์œจ๊ณผ ์ „๊ธฐํ™”ํ•™์  ๋ฐ˜์‘ ํ™œ์„ฑ๋„๋ฅผ ํ–ฅ์ƒ์‹œํ‚ค๋Š” ๋ฐ ๊ธฐ์—ฌํ•  ์ˆ˜ ์žˆ๋‹ค[15]. MOF์˜ ํ™œ์šฉ ๋ฐฉ๋ฒ•์—๋Š” ํฌ์ƒ ํ…œํ”Œ๋ฆฟ(sacrificial template)[16-18], ๊ธˆ์† ์ง€์ง€ ํ…œํ”Œ๋ฆฟ(metal support templating)[19], ๋„ํ•‘(doping) [20] ๋“ฑ์ด ์žˆ์œผ๋ฉฐ, ๊ทธ์ค‘ ๊ธˆ์† ์ง€์ง€ ํ…œํ”Œ๋ฆฟ ๋ฐฉ๋ฒ•์€ 3์ฐจ์› ๋‹ค๊ณต์„ฑ ๊ตฌ์กฐ๋ฅผ ์œ ์ง€ํ•˜๋ฉด์„œ ๋„“์€ ๋ฐ˜์‘ ํ‘œ๋ฉด์ ์„ ์ œ๊ณตํ•˜๊ณ , ํ™œ์„ฑ ๋ฌผ์งˆ์˜ ํ™œ์šฉ๋„๋ฅผ ๋†’์ด๋ฉฐ, ๋ฐ˜์‘ ์ค‘ ์ž…์ž ์‘์ง‘์„ ์–ต์ œํ•˜์—ฌ ์ „๊ทน์˜ ๋‚ด๊ตฌ์„ฑ์„ ๊ฐœ์„ ํ•  ์ˆ˜ ์žˆ๋‹ค๊ณ  ์•Œ๋ ค์ ธ ์žˆ๋‹ค. Metal hydroxide๋Š” ์ผ๋ฐ˜์ ์œผ๋กœ ๋‹ค์–‘ํ•œ ์‚ฐํ™” ์ƒํƒœ, ํ’๋ถ€ํ•œ ์›์†Œ ๊ฐ€์šฉ์„ฑ, ๊ทธ๋ฆฌ๊ณ  ์ „ํ•˜ ์ „๋‹ฌ์— ์œ ๋ฆฌํ•œ ๊ตฌ์กฐ์  ํŠน์„ฑ์œผ๋กœ ์ธํ•ด ์Šˆํผ์ปคํŒจ์‹œํ„ฐ ์ „๊ทน ์†Œ์žฌ๋กœ ๋„๋ฆฌ ํ™œ์šฉ๋˜๊ณ  ์žˆ๋‹ค. ๊ทธ์ค‘ Cu(OH)2๋Š” ํ•ฉ์„ฑ์ด ๊ฐ„๋‹จํ•˜๊ณ  ๋น„์šฉ์ด ์ €๋ ดํ•  ๋ฟ ์•„๋‹ˆ๋ผ, ๋›ฐ์–ด๋‚œ ์ „๊ธฐํ™”ํ•™์  ํŠน์„ฑ๊ณผ ์šฐ์ˆ˜ํ•œ ์ „๊ธฐ ์ „๋„์„ฑ์„ ๊ฐ–์ถ”์–ด ์šฐ์ˆ˜ํ•œ ์Šˆํผ์ปคํŒจ์‹œํ„ฐ ์ „๊ทน ์†Œ์žฌ๋กœ ํ‰๊ฐ€๋ฉ๋‹ˆ๋‹ค. ๋˜ํ•œ, ๋น„์ •์งˆ ๊ตฌ์กฐ๋Š” ์žฅ๊ธฐ์ ์ธ ๊ฒฐ์ • ๊ตฌ์กฐ(long-range crystalline order)๊ฐ€ ํ˜•์„ฑ๋˜์ง€ ์•Š์€ ์ƒํƒœ๋กœ, ๋‹ค์ˆ˜์˜ ๊ฒฐํ•จ(defects)๊ณผ ๊ตฌ์กฐ์  ๋ถˆ๊ทœ์น™์„ฑ(disordered regions)์„ ํ†ตํ•ด ์ „๊ธฐํ™”ํ•™์  ํ™œ์„ฑ ์‚ฌ์ดํŠธ(active site)๋ฅผ ํ’๋ถ€ํ•˜๊ฒŒ ์ œ๊ณตํ•œ๋‹ค[21,22]. ์ด๋Ÿฌํ•œ ๊ฒฐํ•จ์€ ์ด์˜จ์˜ ํ™•์‚ฐ ๊ฑฐ๋ฆฌ๋ฅผ ๋‹จ์ถ•์‹œํ‚ค๊ณ  ์‚ฐํ™”โ€“ํ™˜์› ๋ฐ˜์‘์„ ์ด‰์ง„ํ•˜์—ฌ pseudocapacitor ์„ฑ๋Šฅ ํ–ฅ์ƒ์— ๊ธฐ์—ฌํ•œ๋‹ค[22]. ๋”ฐ๋ผ์„œ, ๋น„์ •์งˆ ๊ตฌ์กฐ๋Š” ์Šˆํผ์ปคํŒจ์‹œํ„ฐ ์ „๊ทน์—์„œ ์ „ํ•˜ ์ €์žฅ ์šฉ๋Ÿ‰๊ณผ ๋ฐ˜์‘ ์†๋„๋ฅผ ๋™์‹œ์— ๊ฐœ์„ ํ•  ์ˆ˜ ์žˆ๋Š” ์œ ๋งํ•œ ์„ค๊ณ„ ์ „๋žต์œผ๋กœ ์ฃผ๋ชฉ๋ฐ›๊ณ  ์žˆ๋‹ค.

๋ณธ ์—ฐ๊ตฌ์—์„œ๋Š” ์šฉ๋งค์—ด ํ•ฉ์„ฑ๋ฒ•(solvothermal method)์„ ์ด์šฉํ•˜์—ฌ ZIF-67 ํ‘œ๋ฉด์— ๋น„์ •์งˆ ๊ตฌ์กฐ์˜ Cu(OH)2๊ฐ€ ์„ฑ์žฅํ•œ ๋ณตํ•ฉ์ฒด(Cu(OH)2@ZIF-67)๋ฅผ ํ•ฉ์„ฑํ•˜์˜€๋‹ค. ํ•ฉ์„ฑ๋œ Cu(OH)2@ZIF-67๋Š” ๋น„์ •์งˆ Cu(OH)2๊ฐ€ ์ œ๊ณตํ•˜๋Š” ๋‹ค์ˆ˜์˜ ํ™œ์„ฑ ์‚ฌ์ดํŠธ๋ฅผ ํ†ตํ•ด ์Šˆ๋„์ปคํŒจ์‹œํ„ด์Šค(pseudocapacitance)๋ฅผ ํšจ๊ณผ์ ์œผ๋กœ ํ–ฅ์ƒ์‹œ์ผฐ๋‹ค. ๊ทธ ๊ฒฐ๊ณผ, Cu(OH)2@ZIF-67๋Š” ZIF-67 ๋Œ€๋น„ ํ˜„์ €ํžˆ ๋†’์€ ๋น„์ •์ „์šฉ๋Ÿ‰(specific capacitance)์„ ๋‚˜ํƒ€๋ƒˆ์œผ๋ฉฐ, ์ „ ์ถœ๋ ฅ ๋ฒ”์œ„์—์„œ ์•ˆ์ •์ ์ธ ์—๋„ˆ์ง€ ๋ฐ€๋„๋ฅผ ์œ ์ง€ํ•˜์˜€๋‹ค.

2. ์‹คํ—˜ ๋ฐฉ๋ฒ•

2.1 ZIF-67 ํ•ฉ์„ฑ

ZIF-67์€ ์„ ํ–‰ ์—ฐ๊ตฌ์—์„œ ๋ณด๊ณ ๋œ ๋ฐฉ๋ฒ•์„ ์ผ๋ถ€ ๋ณ€ํ˜•ํ•˜์—ฌ ํ•ฉ์„ฑํ•˜์˜€๋‹ค. Co(NO3)2ยท6H2O 0.6 g๊ณผ 2-methylimidazole 1.242 g์„ ๊ฐ๊ฐ 30 mL์˜ ๋ฉ”ํƒ„์˜ฌ์— ์šฉํ•ดํ•˜์˜€๋‹ค. ์ดํ›„, 2-methylimidazole ์šฉ์•ก์„ 700 rpm์—์„œ ๊ต๋ฐ˜ ์ค‘์ธ Co(NO3)2 ์šฉ์•ก์— ์ฒจ๊ฐ€ํ•œ ๋’ค, ๊ต๋ฐ˜ ์†๋„๋ฅผ 200 rpm์œผ๋กœ ์ค„์ด๊ณ  90๋ถ„๊ฐ„ ๋ฐ˜์‘์„ ์ง„ํ–‰ํ•˜์˜€๋‹ค. ํ•ฉ์„ฑ๋œ ์ƒ์„ฑ๋ฌผ์€ ์—ฌ๊ณผํ•˜์—ฌ ํšŒ์ˆ˜ํ•˜๊ณ , ์—ํƒ„์˜ฌ๋กœ ์„ธ์ฒ™ํ•œ ํ›„ ์ƒ์˜จ์—์„œ ๊ฑด์กฐํ•˜์˜€๋‹ค.

2.2 Cu(OH)2@ZIF-67 ํ•ฉ์„ฑ

Cu(OH)2@ZIF-67์€ ์šฉ๋งค์—ด ํ•ฉ์„ฑ๋ฒ•์„ ํ†ตํ•ด ์ œ์กฐํ•˜์˜€๋‹ค. ์•ž์„œ ํ•ฉ์„ฑํ•œ ZIF-67 100 mg๊ณผ Cu(NO3)2ยท6H2O 100 mg์„ ์—ํƒ„์˜ฌ 60 mL์— ์šฉํ•ดํ•œ ํ›„, 500 rpm์—์„œ 2์‹œ๊ฐ„ ๋™์•ˆ ๊ต๋ฐ˜ํ•˜์˜€๋‹ค. ๊ต๋ฐ˜์ด ์™„๋ฃŒ๋œ ์šฉ์•ก์„ ํ…Œํ”Œ๋ก  ๋ผ์ด๋„ˆ๊ฐ€ ์žฅ์ฐฉ๋œ ์˜คํ† ํด๋ ˆ์ด๋ธŒ์— ์˜ฎ๊ฒจ 85 ยฐC์—์„œ 6์‹œ๊ฐ„ ๋™์•ˆ ๋ฐ˜์‘์‹œ์ผฐ๋‹ค. ๋ฐ˜์‘์ด ์ข…๋ฃŒ๋œ ์ƒ์„ฑ๋ฌผ์€ ์—ฌ๊ณผ๋ฅผ ํ†ตํ•ด ํšŒ์ˆ˜ํ•œ ๋’ค ์—ํƒ„์˜ฌ๋กœ ์„ธ์ฒ™ํ•˜๊ณ , ์ƒ์˜จ์—์„œ ๊ฑด์กฐํ•˜์˜€๋‹ค.

2.3 ๋ฌผ๋ฆฌํ™”ํ•™์  ํŠน์„ฑ ๋ถ„์„

ํ‘œ๋ฉด ํ˜•์ƒ์€ ์ „๊ณ„ ๋ฐฉ์‚ฌ ์ฃผ์‚ฌ์ „์žํ˜„๋ฏธ๊ฒฝ(FE-SEM, CZ/MIRAI LMH, TESCAN)์„ ์‚ฌ์šฉํ•˜์—ฌ ๋ถ„์„๋˜์—ˆ๋‹ค. ์ข€ ๋” ์ •๋ฐ€ํžˆ ํ˜•์ƒ ๋ถ„์„์„ ํ•˜๊ธฐ ์œ„ํ•ด์„œ ์ „๊ณ„ ๋ฐฉ์‚ฌ ํˆฌ๊ณผ์ „์žํ˜„๋ฏธ๊ฒฝ(FE-TEM, TALOS F200X, Thermo Fisher Scientific, USA)๋ฅผ ํ™œ์šฉํ•˜์—ฌ ๋ถ„์„๋˜์—ˆ๋‹ค. ๊ฒฐ์ • ๊ตฌ์กฐ๋Š” XRD(XRD, Ultima IV, Rigaku)์„ ์‚ฌ์šฉํ•˜์—ฌ ๋ถ„๋‹น 2ยฐ๋กœ 5ยฐ๋ถ€ํ„ฐ 80ยฐ๊นŒ์ง€ ๋ถ„์„๋˜์—ˆ๋‹ค. ํ‘ธ๋ฆฌ์— ๋ณ€ํ™˜ ์ ์™ธ์„  ๋ถ„๊ด‘(FTIR)์€ Cary 670(Main Bench)์™€ Cary 620(Microscope)์„ ์‚ฌ์šฉํ•˜์—ฌ ๋ถ„์„๋˜์—ˆ๋‹ค.

2.4 ์ „๊ธฐํ™”ํ•™์  ํŠน์„ฑ ๋ถ„์„

๋ชจ๋“  ์ „๊ธฐํ™”ํ•™ ์ธก์ •์€ Potentiostat(BP2, WonAtech)์„ ์‚ฌ์šฉํ•˜์—ฌ 3์ „๊ทน ์‹œ์Šคํ…œ์—์„œ ์ˆ˜ํ–‰ํ•˜์˜€๋‹ค. ์ „ํ•ด์งˆ, ๊ธฐ์ค€ ์ „๊ทน, ์ƒ๋Œ€ ์ „๊ทน์œผ๋กœ ๊ฐ๊ฐ 6 M KOH ์ˆ˜์šฉ์•ก, Hg/HgO ์ „๊ทน, ํƒ„์†Œ ๋ง‰๋Œ€๋ฅผ ์‚ฌ์šฉํ•˜์˜€์œผ๋ฉฐ, ์ž‘๋™ ์ „๊ทน์œผ๋กœ๋Š” ์ œ์กฐํ•œ ์ „๊ทน์„ ์‚ฌ์šฉํ•˜์˜€๋‹ค. ์ „๊ทน์€ ํ•ฉ์„ฑ๋œ ๋ฌผ์งˆ์„ ์ƒ์šฉ ๋‹ˆ์ผˆ ํผ(Ni foam) ๊ธฐํŒ์— 2 mg/cm2์˜ ๋กœ๋”ฉ๋Ÿ‰์œผ๋กœ ์ฝ”ํŒ…ํ•˜์—ฌ ์ œ์กฐํ•˜์˜€๋‹ค. ์ฝ”ํŒ… ์ „, ๋‹ˆ์ผˆ ํผ ํ‘œ๋ฉด์˜ ์‚ฐํ™”์ธต ์ œ๊ฑฐ๋ฅผ ์œ„ํ•ด 5 M HCl ์ˆ˜์šฉ์•ก์—์„œ 15๋ถ„๊ฐ„ ์ดˆ์ŒํŒŒ ์„ธ์ฒ™(ultrasonication)์„ ์‹ค์‹œํ•œ ํ›„, ์ฆ๋ฅ˜์ˆ˜๋กœ 2ํšŒ ์„ธ์ฒ™ํ•˜์˜€๋‹ค. ์ „๊ทน ์ž‰ํฌ๋Š” ์ ์ •๋Ÿ‰์˜ Nafion(5 wt%), ์•„์ด์†Œํ”„๋กœํ•„ ์•Œ์ฝ”์˜ฌ(IPA), ์ฆ๋ฅ˜์ˆ˜๋ฅผ ํ˜ผํ•ฉํ•œ ๋’ค 30๋ถ„๊ฐ„ ์ดˆ์ŒํŒŒ ๋ถ„์‚ฐํ•˜์—ฌ ์ค€๋น„ํ•˜์˜€๋‹ค.

์ˆœํ™˜ ์ „์••์ „๋ฅ˜๋ฒ•(Cyclic Voltammetry, CV)์€ 0โ€“0.5V ๋ฒ”์œ„์—์„œ ์Šค์บ” ์†๋„ 10, 20, 30, 40, 80 mV/s๋กœ ์ธก์ •ํ•˜์˜€๋‹ค. ์ •์ „๋ฅ˜ ์ถฉยท๋ฐฉ์ „(Galvanostatic Chargeโ€“Discharge, GCD) ๋ถ„์„์€ 0โ€“0.5 V ๋ฒ”์œ„์—์„œ ์ „๋ฅ˜ ๋ฐ€๋„ 3, 4, 5, 10 A/g๋กœ ์ˆ˜ํ–‰ํ•˜์˜€๋‹ค. ๋น„์ •์ „์šฉ๋Ÿ‰(specific capacitance, Csp)์€ ๋‹ค์Œ ์‹์„ ์‚ฌ์šฉํ•˜์—ฌ GCD ๊ณก์„ ์œผ๋กœ๋ถ€ํ„ฐ ๊ณ„์‚ฐํ•˜์˜€๋‹ค[23].

C s p = I ร— t V ร— m ( F / g )

์—ฌ๊ธฐ์„œ, Csp(F/g)๋Š” ๋น„์ •์ „์šฉ๋Ÿ‰, I(A)๋Š” ๋ฐฉ์ „ ์ „๋ฅ˜, t(s)๋Š” ๋ฐฉ์ „ ์‹œ๊ฐ„, V(V)๋Š” ์ „์œ„ ๋ฒ”์œ„, m(g)๋Š” ํ™œ์„ฑ ๋ฌผ์งˆ์˜ ์งˆ๋Ÿ‰์ด๋‹ค. ๋น„์—๋„ˆ์ง€๋ฐ€๋„(specific energy, E)์™€ ๋น„์ถœ๋ ฅ(specific power, P)์€ ๋‹ค์Œ ์‹์„ ์ด์šฉํ•˜์—ฌ ๊ณ„์‚ฐํ•˜์˜€๋‹ค[23].

E = C ร— V 2 7.2 ( W h / k g )
P = 3600 ร— E t ( W / k g )

์—ฌ๊ธฐ์„œ, E(Wh/kg)๋Š” ๋น„์—๋„ˆ์ง€๋ฐ€๋„, C(F/g)๋Š” ๋น„์ •์ „์šฉ๋Ÿ‰, V(V)๋Š” ์ „์œ„ ๋ฒ”์œ„, t(s)๋Š” ๋ฐฉ์ „ ์‹œ๊ฐ„์„ ๋‚˜ํƒ€๋‚ธ๋‹ค. ์‚ฌ์ดํด ์ˆ˜๋ช…(cycle life) ํ‰๊ฐ€๋Š” ์ „๋ฅ˜ ๋ฐ€๋„ 10 A/g ์กฐ๊ฑด์—์„œ 1000ํšŒ ์ถฉยท๋ฐฉ์ „ ์‚ฌ์ดํด์„ ์ˆ˜ํ–‰ํ•˜์—ฌ ์ง„ํ–‰ํ•˜์˜€๋‹ค. ์ž„ํ”ผ๋˜์Šค ๋ถ„์„์€ 20 mV ์ง„ํญ์œผ๋กœ ์ˆ˜ํ–‰๋˜์—ˆ์œผ๋ฉฐ, ์ฃผํŒŒ์ˆ˜ ๋ฒ”์œ„๋Š” 100 kHz์—์„œ 1 Hz๊นŒ์ง€ ์„ค์ •ํ•˜์˜€๋‹ค.

3. ๊ฒฐ๊ณผ ๋ฐ ๊ณ ์ฐฐ

3.1 ๋ฌผ๋ฆฌํ™”ํ•™์  ํŠน์„ฑ ๋ถ„์„

Cu(OH)2@ZIF-67์€ ์šฉ๋งค์—ด ํ•ฉ์„ฑ๋ฒ•(solvothermal method)์„ ์ด์šฉํ•˜์—ฌ ํ•ฉ์„ฑํ•˜์˜€์œผ๋ฉฐ, ํ•ฉ์„ฑ ๊ณผ์ •์€ ๊ทธ๋ฆผ 1์— ๋‚˜ํƒ€๋‚ด์—ˆ๋‹ค. ์‹œ๋ฃŒ์˜ ํ‘œ๋ฉด ํ˜•์ƒ์€ ์ „๊ณ„ ๋ฐฉ์‚ฌ ์ฃผ์‚ฌ์ „์žํ˜„๋ฏธ๊ฒฝ(FE-SEM) ๋ถ„์„์„ ํ†ตํ•ด ํ™•์ธํ•˜์˜€๋‹ค(๊ทธ๋ฆผ 2(a), (b)). ZIF-67์€ ํŠน์œ ์˜ rhombic dodecahedral ๊ตฌ์กฐ๋กœ ๊ด€์ฐฐ๋˜์—ˆ์œผ๋ฉฐ[24], Cu(OH)2@ZIF-67์—์„œ๋Š” ZIF-67ํ‘œ๋ฉด์— ๋‚˜๋…ธ์‹œํŠธ ํ˜•ํƒœ์˜ Cu(OH)2๊ฐ€ ์„ฑ์žฅํ•œ ๊ฒƒ์ด ๊ด€์ฐฐ๋˜์—ˆ๋‹ค. ์ด๋Ÿฌํ•œ 3์ฐจ์› ๋‚˜๋…ธ์‹œํŠธ ๊ตฌ์กฐ๋Š” ๋†’์€ ๋น„ํ‘œ๋ฉด์ ์„ ์ œ๊ณตํ•˜์—ฌ EDLC ํŠน์„ฑ ํ–ฅ์ƒ์— ๊ธฐ์—ฌํ•  ์ˆ˜ ์žˆ๋‹ค[25]. ๋ณด๋‹ค ์ •๋ฐ€ํ•œ ๋ถ„์„์„ ์œ„ํ•ด ํˆฌ๊ณผ์ „์žํ˜„๋ฏธ๊ฒฝ(TEM) ๊ด€์ฐฐ์„ ์ˆ˜ํ–‰ํ•˜์˜€๋‹ค. TEM ์ด๋ฏธ์ง€(๊ทธ๋ฆผ 2(c))์—์„œ๋„ ZIF-67 ์ž…์ž ํ‘œ๋ฉด์— Cu(OH)2 ๋‚˜๋…ธ์‹œํŠธ๊ฐ€ ์„ฑ์žฅํ•œ ํ˜•ํƒœ๊ฐ€ ํ™•์ธ๋˜์—ˆ์œผ๋ฉฐ, ์ด๋Š” SEM ๋ถ„์„ ๊ฒฐ๊ณผ์™€ ์ผ์น˜ํ•œ๋‹ค. ์„ ํƒ์˜์—ญ ์ „์žํšŒ์ ˆ(SAED) ํŒจํ„ด์—์„œ๋Š” ๋šœ๋ ทํ•œ ํšŒ์ ˆ ๋ง์ด ๊ด€์ฐฐ๋˜์ง€ ์•Š์•„ ์ „ํ˜•์ ์ธ ๋น„์ •์งˆ ๊ตฌ์กฐ์ž„์„ ๋‚˜ํƒ€๋‚ด์—ˆ์œผ๋ฉฐ[26], ๊ณ ํ•ด์ƒ๋„ TEM(HR-TEM) ์ด๋ฏธ์ง€(๊ทธ๋ฆผ 2(d))์—์„œ๋„ ๋ช…ํ™•ํ•œ ๊ฒฉ์ž ๋ฌด๋Šฌ๊ฐ€ ๊ด€์ฐฐ๋˜์ง€ ์•Š์•„ Cu(OH)2๊ฐ€ ๋น„์ •์งˆ ๊ตฌ์กฐ๋ฅผ ์ง€๋‹˜์„ ํ™•์ธํ•˜์˜€๋‹ค[27]. SAED ํŒจํ„ด์—์„œ ZIF-67 ํšŒ์ ˆ ๋ฌด๋Šฌ๊ฐ€ ํ™•์ธ๋˜์ง€ ์•Š์€ ์ด์œ ๋Š” ZIF-67์ด ๊ฐ•ํ•œ ์ „์ž ๋น”์— ์‰ฝ๊ฒŒ ์†์ƒ๋˜๊ธฐ ๋•Œ๋ฌธ์ด๋‹ค. ์—๋„ˆ์ง€ ๋ถ„์‚ฐํ˜• X์„  ๋ถ„๊ด‘(EDS) ๋งคํ•‘ ๊ฒฐ๊ณผ, Cu์™€ Co๊ฐ€ ๋…๋ฆฝ์ ์œผ๋กœ ๋ถ„ํฌํ•˜๋Š” ๊ฒƒ์ด ํ™•์ธ๋˜์—ˆ์œผ๋ฉฐ, ์ด๋Š” Cu(OH)2๊ฐ€ ZIF-67 ํ‘œ๋ฉด์— ์„ฑ์žฅํ•˜์˜€์Œ์„ ๋’ท๋ฐ›์นจํ•œ๋‹ค.

ํ•ฉ์„ฑ๋œ ์‹œ๋ฃŒ์˜ ๊ฒฐ์ • ๊ตฌ์กฐ๋Š” X์„  ํšŒ์ ˆ(XRD) ๋ถ„์„์„ ํ†ตํ•ด ํ™•์ธํ•˜์˜€๋‹ค(๊ทธ๋ฆผ 3(a)). ZIF-67์€ ์•ฝ 7.3ยฐ, 10.4ยฐ, 12.7ยฐ, 18.0ยฐ์—์„œ ๋šœ๋ ทํ•œ ํšŒ์ ˆ ํ”ผํฌ๋ฅผ ๋‚˜ํƒ€๋ƒˆ์œผ๋ฉฐ, ์ด๋Š” ๊ฐ๊ฐ ZIF-67์˜ (011), (002), (112), (222) ๋ฉด์— ํ•ด๋‹นํ•œ๋‹ค[28,29]. Cu(OH)2@ZIF-67์€ ZIF-67 ํ”ผํฌ์˜ ๊ฐ•๋„๊ฐ€ ๊ฐ์†Œํ•˜๊ณ  ํญ์ด ๋„“์–ด์กŒ๋Š”๋ฐ, ์ด๋Š” ํ•ฉ์„ฑ ๊ณผ์ •์—์„œ ZIF-67์˜ ๊ฒฐ์ •์„ฑ์ด ์ €ํ•˜๋˜์—ˆ์Œ์„ ์˜๋ฏธํ•œ๋‹ค[30,31]. ๋˜ํ•œ, Cu(OH)2์— ํ•ด๋‹นํ•˜๋Š” ํšŒ์ ˆ ํ”ผํฌ๊ฐ€ ๊ด€์ฐฐ๋˜์ง€ ์•Š์•„ Cu(OH)2๊ฐ€ ๋น„์ •์งˆ ๊ตฌ์กฐ๋กœ ์กด์žฌํ•จ์„ ํ™•์ธํ•  ์ˆ˜ ์žˆ์—ˆ๋‹ค[32]. ZIF-67์˜ ๋‚ฎ์€ ๊ฒฐ์ •์„ฑ๊ณผ Cu(OH)2์˜ ๋น„์ •์งˆ ๊ตฌ์กฐ๋Š” ๋‹ค์ˆ˜์˜ ์ž…๊ณ„๋ฅผ ํ˜•์„ฑํ•˜๋ฉฐ, ์ด๋Š” ๋ฐ˜์‘๋ฌผ ํก์ฐฉ ์‚ฌ์ดํŠธ๋กœ ์ž‘์šฉํ•˜์—ฌ ์Šˆ๋„์ปคํŒจ์‹œํ„ด์Šค๋ฅผ ํ–ฅ์ƒ์‹œํ‚ค๋Š”๋ฐ ๊ธฐ์—ฌํ•  ์ˆ˜ ์žˆ๋‹ค[21].

Cu(OH)2์˜ ์กด์žฌ๋ฅผ ์ถ”๊ฐ€๋กœ ํ™•์ธํ•˜๊ธฐ ์œ„ํ•ด ํ‘ธ๋ฆฌ์— ๋ณ€ํ™˜ ์ ์™ธ์„  ๋ถ„๊ด‘(FTIR) ๋ถ„์„์„ ์ˆ˜ํ–‰ํ•˜์˜€๋‹ค(๊ทธ๋ฆผ 3(b)). ZIF-67๊ณผ Cu(OH)2@ZIF-67 ๋ชจ๋‘์—์„œ 1305 cm-1๊ณผ 1144 cm-1 ๋ถ€๊ทผ์—์„œ ๊ณตํ†ต ํ”ผํฌ๊ฐ€ ๋‚˜ํƒ€๋‚ฌ์œผ๋ฉฐ, ์ด๋Š” ZIF-67์˜ imidazole ring์— ํ•ด๋‹นํ•˜๋Š” ๊ฒฐํ•ฉ ์ง„๋™์„ ์˜๋ฏธํ•œ๋‹ค[33]. ์ถ”๊ฐ€์ ์œผ๋กœ, 1597 cm-1๊ณผ 1416 cm-1๋„ ๊ณตํ†ต์ ์œผ๋กœ ๊ด€์ฐฐ๋˜์—ˆ์œผ๋ฉฐ, ์ด๋Š” ZIF-67์˜ C=N ๊ฒฐํ•ฉ ์ง„๋™์— ํ•ด๋‹น๋œ๋‹ค. ๋ฐ˜๋ฉด, Cu(OH)2@ZIF-67์—์„œ๋Š” ZIF-67์—์„œ ๊ด€์ฐฐ๋˜์ง€ ์•Š๋Š” 3400 cm-1 ๋ถ€๊ทผ์˜ ๋„“์€ ํ”ผํฌ์™€ 1110 cm-1 ๋ถ€๊ทผ์˜ ์ƒˆ๋กœ์šด ํ”ผํฌ๊ฐ€ ๋‚˜ํƒ€๋‚ฌ๋‹ค. ์ด๋Š” ๊ฐ๊ฐ ํก์ฐฉ๋œ ๋ฌผ ๋ถ„์ž์˜ Oโ€“H ๊ฒฐํ•ฉ ์ง„๋™๊ณผ Cuโ€“OH ๊ฒฐํ•ฉ ์ง„๋™์— ํ•ด๋‹นํ•˜๋ฉฐ, Cu(OH)2์˜ ์กด์žฌ๋ฅผ ๋’ท๋ฐ›์นจํ•œ๋‹ค[34,35]. ์ด๋Ÿฌํ•œ ๋ถ„์„ ๊ฒฐ๊ณผ๋Š” Cu(OH)2@ZIF-67๊ฐ€ ZIF-67๊ณผ Cu(OH)2๋กœ ๊ตฌ์„ฑ๋˜์–ด ์žˆ์Œ์„ ๋ช…ํ™•ํžˆ ๋ณด์—ฌ์ค€๋‹ค.

3.2 ์ „๊ธฐํ™”ํ•™์  ํŠน์„ฑ ๋ถ„์„

Cu(OH)2@ZIF-67๊ณผ ZIF-67์˜ ์ „๊ธฐํ™”ํ•™์  ์„ฑ๋Šฅ์€ ์ˆœํ™˜ ์ „์••์ „๋ฅ˜๋ฒ•(Cyclic Voltammetry, CV)์„ ํ†ตํ•ด ํ‰๊ฐ€๋˜์—ˆ๋‹ค. ๊ทธ๋ฆผ 4(a)์™€ 4(b)๋Š” ์„œ๋กœ ๋‹ค๋ฅธ ์ฃผ์‚ฌ ์†๋„์—์„œ ์ธก์ •๋œ ๋‘ ์‹œ๋ฃŒ์˜ CV ๊ณก์„ ์„ ๋‚˜ํƒ€๋‚ธ๋‹ค. ์ผ๋ฐ˜์ ์œผ๋กœ CV ๊ณก์„ ์ด ์ง์‚ฌ๊ฐํ˜• ํ˜•ํƒœ๋ฅผ ๋ณด์ด๋ฉด ์ „๊ธฐ์ด์ค‘์ธต ์ปคํŒจ์‹œํ„ด์Šค(Electric Double-Layer Capacitance, EDLC) ํŠน์„ฑ์„ ์˜๋ฏธํ•œ๋‹ค[36]. ๋‘ ์‹œ๋ฃŒ ๋ชจ๋‘ ์™„์ „ํžˆ ์ง์‚ฌ๊ฐํ˜• ํ˜•ํƒœ๋Š” ์•„๋‹ˆ์ง€๋งŒ, ๋น„์ง์‚ฌ๊ฐํ˜• ํŠน์„ฑ์„ ๋ณด์—ฌ ์Šˆ๋„์ปคํŒจ์‹œํ„ด์Šค(pseudocapacitance) ๊ธฐ์—ฌ๊ฐ€ ์žˆ์Œ์„ ํ™•์ธํ•  ์ˆ˜ ์žˆ์—ˆ๋‹ค.

๋˜ํ•œ, CV ๊ณก์„ ์˜ ๋ฉด์ ์€ ์šฉ๋Ÿ‰๊ณผ ๋น„๋ก€ํ•˜๋ฏ€๋กœ, ๊ทธ๋ฆผ 4(a)์™€ 4(b) ๋น„๊ต ๊ฒฐ๊ณผ Cu(OH)2@ZIF-67๊ฐ€ ZIF-67๋ณด๋‹ค ๋„“์€ ๋ฉด์ ์„ ๋‚˜ํƒ€๋‚ด์–ด ๋” ๋†’์€ ์ „ํ•˜ ์ €์žฅ ์šฉ๋Ÿ‰์„ ๊ฐ–๋Š” ๊ฒƒ์œผ๋กœ ํ‰๊ฐ€๋˜์—ˆ๋‹ค. ์ „๊ธฐํ™”ํ•™์  ์„ฑ๋Šฅ์„ ์ถ”๊ฐ€๋กœ ๊ฒ€์ฆํ•˜๊ธฐ ์œ„ํ•ด ์ •์ „๋ฅ˜ ์ถฉยท๋ฐฉ์ „(Galvanostatic Chargeโ€“Discharge, GCD) ๋ถ„์„์„ ์ˆ˜ํ–‰ํ•˜์˜€๋‹ค(๊ทธ๋ฆผ 4(c), (d)). GCD ๊ณก์„ ์—์„œ ๋ฐฉ์ „ ์‹œ๊ฐ„์ด ๊ธธ์ˆ˜๋ก ์ „ํ•˜ ์ €์žฅ ์šฉ๋Ÿ‰์ด ํฌ๋ฉฐ, Cu(OH)2@ZIF-67์˜ ๋ฐฉ์ „ ์‹œ๊ฐ„์ด ZIF-67๋ณด๋‹ค ๊ธธ๊ฒŒ ๋‚˜ํƒ€๋‚˜ ๋” ๋†’์€ ์ „ํ•˜ ์ €์žฅ ์šฉ๋Ÿ‰์„ ๋ณด์œ ํ•จ์„ ํ™•์ธํ•˜์˜€๋‹ค. ์ด๋Ÿฌํ•œ ์„ฑ๋Šฅ ํ–ฅ์ƒ์€ ๋น„์ •์งˆ ๊ตฌ์กฐ์˜ Cu(OH)2๊ฐ€ ๋‹ค์ˆ˜์˜ ๋ฐ˜์‘๋ฌผ ํก์ฐฉ ์‚ฌ์ดํŠธ๋ฅผ ์ œ๊ณตํ•˜์—ฌ ์‚ฐํ™”ยทํ™˜์› ๋ฐ˜์‘์„ ์ด‰์ง„ ์‹œ์ผฐ๊ธฐ ๋•Œ๋ฌธ์œผ๋กœ ํŒ๋‹จ๋œ๋‹ค[22]. ์„œ๋กœ ๋‹ค๋ฅธ ์ „๋ฅ˜ ๋ฐ€๋„์—์„œ์˜ ๋ฐฉ์ „ ๊ณก์„ ์„ ์ด์šฉํ•˜์—ฌ ๋น„์ •์ „์šฉ๋Ÿ‰(specific capacitance)์„ ๊ณ„์‚ฐํ•˜์˜€๋‹ค(๊ทธ๋ฆผ 5(a)). ๋‘ ์‹œ๋ฃŒ ๋ชจ๋‘ ์ „๋ฅ˜ ๋ฐ€๋„๊ฐ€ ์ฆ๊ฐ€ํ•จ์— ๋”ฐ๋ผ ๋น„์ •์ „์šฉ๋Ÿ‰์ด ๊ฐ์†Œํ•˜์˜€์œผ๋ฉฐ, ์ด๋Š” ๋†’์€ ์ถฉยท๋ฐฉ์ „ ์†๋„์—์„œ ์ „๊ทน ๋ฌผ์งˆ์˜ ํ™œ์šฉ๋„๊ฐ€ ์ €ํ•˜๋˜๊ธฐ ๋•Œ๋ฌธ์œผ๋กœ ํ•ด์„๋œ๋‹ค. ๊ฐ€์žฅ ๋‚ฎ์€ ์ „๋ฅ˜ ๋ฐ€๋„(3 A/g)์—์„œ Cu(OH)2@ZIF-67์€ 168 F/g์˜ ๊ฐ’์„ ๋‚˜ํƒ€๋‚ด์–ด ZIF-67(41.4 F/g)๋ณด๋‹ค ์•ฝ 4๋ฐฐ ๋†’์€ ์šฉ๋Ÿ‰์„ ๊ธฐ๋กํ•˜์˜€๋‹ค.

Ragone plot ๋ถ„์„ ๊ฒฐ๊ณผ(๊ทธ๋ฆผ 5(b))์—์„œ, Cu(OH)2@ZIF-67์€ ์ „ ์ถœ๋ ฅ ๋ฒ”์œ„์—์„œ ZIF-67๋ณด๋‹ค ๋†’์€ ์—๋„ˆ์ง€ ๋ฐ€๋„๋ฅผ ์œ ์ง€ํ•˜์˜€๋‹ค. ์ด๋Š” ๋น„์ •์งˆ ๊ตฌ์กฐ๊ฐ€ ์Šˆํผ์ปคํŒจ์‹œํ„ฐ์˜ ์—๋„ˆ์ง€ ์ €์žฅ ์„ฑ๋Šฅ์„ ํšจ๊ณผ์ ์œผ๋กœ ํ–ฅ์ƒ์‹œ์ผฐ์Œ์„ ์˜๋ฏธํ•œ๋‹ค. ์ „๊ธฐํ™”ํ•™ ์ž„ํ”ผ๋˜์Šค ๋ถ„๊ด‘๋ฒ•(Electrochemical Impedance Spectroscopy, EIS) ๋ถ„์„์„ ํ†ตํ•ด ์ „๊ทน์˜ ์ €ํ•ญ ํŠน์„ฑ์„ ํ‰๊ฐ€ํ•˜์˜€๋‹ค(๊ทธ๋ฆผ 5(c)). Nyquist plot์—์„œ ๋ฐ˜์›์˜ ์ง๊ฒฝ์€ ์ „ํ•˜ ์ „๋‹ฌ ์ €ํ•ญ(Rct)์— ํ•ด๋‹นํ•˜๋ฉฐ[37], Cu(OH)2@ZIF-67์˜ ๋ฐ˜์›์ด ZIF-67 ๋ณด๋‹ค ์ž‘๊ฒŒ ๋‚˜ํƒ€๋‚˜ ๋” ๋‚ฎ์€ Rct ๊ฐ’์„ ๋ณด์œ ํ•จ์ด ํ™•์ธ๋˜์—ˆ๋‹ค. ๋˜ํ•œ, ์ €์ฃผํŒŒ ์˜์—ญ์—์„œ Cu(OH)2@ZIF-67์˜ ๊ณก์„  ๊ธฐ์šธ๊ธฐ๊ฐ€ ๋” ๊ฐ€ํŒŒ๋ฅด๊ฒŒ ๋‚˜ํƒ€๋‚˜ ํ™•์‚ฐ ์ €ํ•ญ์ด ๋‚ฎ๊ณ  ์ด์ƒ์ ์ธ ์ปคํŒจ์‹œํ„ฐ ๊ฑฐ๋™์— ๊ฐ€๊นŒ์šด ํŠน์„ฑ์„ ๋ณด์—ฌ์ฃผ์—ˆ๋‹ค[38]. ๋‚ด๊ตฌ๋„๋ฅผ ํ™•์ธํ•˜๊ธฐ ์œ„ํ•ด์„œ ์‚ฌ์ดํด ์ˆ˜๋ช… ํ‰๊ฐ€๋ฅผ ์ˆ˜ํ–‰ํ•˜์˜€๋‹ค(๊ทธ๋ฆผ 5(d)). ์ „๋ฅ˜ ๋ฐ€๋„ 10 A/g์—์„œ 1000ํšŒ ์ถฉยท๋ฐฉ์ „ ์‚ฌ์ดํด์„ ์ˆ˜ํ–‰ํ•œ ๊ฒฐ๊ณผ, Cu(OH)2@ZIF-67๋Š” ์ดˆ๊ธฐ ๋น„์ •์ „์šฉ๋Ÿ‰ ๋Œ€๋น„ ์•ฝ 86%๋ฅผ ์œ ์ง€ํ•˜์—ฌ ์šฐ์ˆ˜ํ•œ ๋‚ด๊ตฌ์„ฑ์„ ๋‚˜ํƒ€๋ƒˆ๋‹ค.

4. ๊ฒฐ ๋ก 

๋ณธ ์—ฐ๊ตฌ์—์„œ๋Š” ๋น„์ •์งˆ ๊ตฌ์กฐ์˜ Cu(OH)2์™€ ZIF-67 ํ‘œ๋ฉด์— ๋‚˜๋…ธ์‹œํŠธ ํ˜•ํƒœ๋กœ ์„ฑ์žฅํ•œ Cu(OH)2/ZIF-67๋ณตํ•ฉ์ฒด(Cu(OH)2@ZIF-67)๋ฅผ ์šฉ๋งค์—ด ํ•ฉ์„ฑ๋ฒ•์œผ๋กœ ํ•ฉ์„ฑํ•˜๊ณ , ์ด๋ฅผ ์Šˆํผ์ปคํŒจ์‹œํ„ฐ ์ „๊ทน ์†Œ์žฌ๋กœ ์ ์šฉํ•˜์˜€๋‹ค. ๋น„์ •์งˆ Cu(OH)2๋Š” ๋‹ค์ˆ˜์˜ ํ™œ์„ฑ ์‚ฌ์ดํŠธ๋ฅผ ์ œ๊ณตํ•˜์—ฌ ์‚ฐํ™”ยทํ™˜์› ๋ฐ˜์‘์„ ์ด‰์ง„ํ•˜๊ณ , ์ „ํ•˜ ์ €์žฅ ์†๋„๋ฅผ ํ–ฅ์ƒ์‹œ์ผฐ๋‹ค. ์ „๊ธฐํ™”ํ•™์  ํ‰๊ฐ€ ๊ฒฐ๊ณผ, Cu(OH)2@ZIF-67๋Š” ZIF-67์— ๋น„ํ•ด ์•ฝ 4๋ฐฐ ๋†’์€ ๋น„์ •์ „์šฉ๋Ÿ‰๊ณผ ์ „ ์ถœ๋ ฅ ๋ฒ”์œ„์—์„œ ์šฐ์ˆ˜ํ•œ ์—๋„ˆ์ง€ ๋ฐ€๋„๋ฅผ ๋‚˜ํƒ€๋ƒˆ์œผ๋ฉฐ, ๋‚ฎ์€ ์ „ํ•˜ ์ „๋‹ฌ ์ €ํ•ญ๊ณผ ์ด์ƒ์ ์ธ ์ปคํŒจ์‹œํ„ฐ ๊ฑฐ๋™์„ ๋ณด์˜€๋‹ค. ๋˜ํ•œ, 1000ํšŒ ์ถฉยท๋ฐฉ์ „ ์‚ฌ์ดํด ํ›„์—๋„ ์ดˆ๊ธฐ ์šฉ๋Ÿ‰์˜ ์•ฝ 86%๋ฅผ ์œ ์ง€ํ•˜์—ฌ ์šฐ์ˆ˜ํ•œ ๋‚ด๊ตฌ์„ฑ์„ ํ™•์ธํ•˜์˜€๋‹ค. ์ด๋Ÿฌํ•œ ๊ฒฐ๊ณผ๋Š” ZIF-67์„ ๊ธˆ์† ์ง€์ง€์ฒด๋กœ ํ™œ์šฉํ•˜๊ณ , ๋น„์ •์งˆ Cu(OH)2๋ฅผ ๋„์ž…ํ•˜๋Š” ์ „๋žต์ด ์Šˆํผ์ปคํŒจ์‹œํ„ฐ ์„ฑ๋Šฅ์„ ํšจ๊ณผ์ ์œผ๋กœ ํ–ฅ์ƒ์‹œํ‚ฌ ์ˆ˜ ์žˆ์Œ์„ ์ž…์ฆํ•œ๋‹ค.

Notes

[1] ๊ฐ์‚ฌ์˜ ๊ธ€

์ด ์„ฑ๊ณผ๋Š” ์ •๋ถ€(๊ณผํ•™๊ธฐ์ˆ ์ •๋ณดํ†ต์‹ ๋ถ€)์˜ ์žฌ์›์œผ๋กœ ํ•œ๊ตญ์—ฐ๊ตฌ์žฌ๋‹จ์˜ ์ง€์›์„ ๋ฐ›์•„ ์ˆ˜ํ–‰๋œ ์—ฐ๊ตฌ์ž„(No. RS-2023-00242344, No. RS-2023-00236572). ๋˜ํ•œ, ์ด ์—ฐ๊ตฌ๋Š”2023๋…„๋„ ์‚ฐ์—…ํ†ต์ƒ์ž์›๋ถ€ ๋ฐ ์‚ฐ์—…๊ธฐ์ˆ ๊ธฐํšํ‰๊ฐ€์›(KEIT) ์—ฐ๊ตฌ๋น„ ์ง€์›์— ์˜ํ•œ ์—ฐ๊ตฌ์ž„(RS-2023-00266568).

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Figures

Fig. 1.

Schematic of the synthetic procedure for Cu(OH)2@ZIF-67.

../../Resources/kim/KJMM.2025.63/kjmm-2025-63-11-913f1.jpg
Fig. 2.

Surface morphology of (a) ZIF-67 and (b) Cu(OH)2@ZIF-67, (c) TEM image and (inset image) SAED pattern of Cu(OH)2@ZIF-67, (d) HR-TEM image and (e) TEM-EDS mapping images of Cu(OH)2@ZIF-67

../../Resources/kim/KJMM.2025.63/kjmm-2025-63-11-913f2.jpg
Fig. 3.

(a) XRD patterns of ZIF-67 and Cu(OH)2@ZIF-67. (b) FTIR spectrum of ZIF-67 and Cu(OH)2@ZIF-67

../../Resources/kim/KJMM.2025.63/kjmm-2025-63-11-913f3.jpg
Fig. 4.

CV curve of (a) ZIF-67 and (b) Cu(OH)2@ZIF-67. GCD plots of (c) ZIF-67 and (d) Cu(OH)2@ZIF-67

../../Resources/kim/KJMM.2025.63/kjmm-2025-63-11-913f4.jpg
Fig. 5.

(a) Specific capacitance of ZIF-67 and Cu(OH)2@ZIF-67. (b) Ragone plots of ZIF-67 and Cu(OH)2@ZIF-67 at different current density. (c) Nyquist plots of ZIF-67 and Cu(OH)2@ZIF-67. (d) Retention of capacitance during durability test of Cu(OH)2@ZIF-67

../../Resources/kim/KJMM.2025.63/kjmm-2025-63-11-913f5.jpg