Polymer electrolyte membrane fuel cell using hydrogen produced by waste aluminum hydration reaction

Abstract

지구 온난화가 심화되면서 이상기후 현상이 빈번하게 발생하고 있으며, 이에 따라 지구 평균기온 상승을 낮추기 위한 노력이 전 세계적으로 진행되고 있다. 수소는 미래 차세대 에너지원으로 화석연료를 대체할 새로운 잠재적 후보로 다양한 분야에서 많은 주목을 받고 있으며, 탄소중립 정책의 핵심으로 떠오르고 있다. 현재 전 세계 수소의 약 75%가 천연가스 개질을 통해 생산되며, 생산 시 발생하는 이산화탄소를 비롯한 생산, 저장 및 운송 비용이 문제가 되고 있다. 본 연구에서는 폐알루미늄과 물의 수화반응을 통해 생산된 수소를 고분자 전해질막 연료전지(PEMFC)에 직접 연료로 공급하여 폐알루미늄의 수소 생산 가능성과 연료전지에 대한 적합여부를 확인하였으며, 알루미늄은 일상생활에서 쉽게 접할 수 있는 알루미늄 캔 (used beverage cans, UBCs), 탈 코팅된 알루미늄 캔 그래뉼 (de-coated Al can granules), 건설용 알루미늄 (construction aluminum materials), 요구르트 뚜껑 (yogurt lids), 고순도 알루미늄 (high-purity aluminum)를 이용하였다. 또한, 연료전지 구동 후 막전극접합체(MEA)의 특성을 분석하기 위해 순환전압전류법(CV), 전기화학적 임피던스 분광분석법(EIS)을 수행하였다. 폐알루미늄 수화반응은 각 종류의 폐알루미늄 5 g과 1, 3, 5 M NaOH 수용액 200 mL로 수행하였다. UBCs, de-coated Al can granules, construction aluminum materials, yogurt lids 및 high-purity aluminum과 5 M NaOH 수용액과 반응했을 때, 각각 6435, 6630, 6540, 5124, 6855 mL의 수소가 발생했으며, 온도는 43, 79, 40, 63, 63 ℃까지 상승하였다. 3 M NaOH 수용액의 경우 수소가 6270, 6580, 6480, 4950, 6710 mL의 수소가 발생했으며, 온도는 38, 76, 37, 55, 32 ℃까지 상승했다. 수화반응을 통해 발생된 수소를 PEMFC에 적용하여 200 Cycle 전후로 전류밀도를 측정한 결과, high-purity hydrogen (99.999%)를 사용했을 때 0.6V의 전류밀도 가 1.25 A/cm2에서 1.20 A/cm2로 감소하였고, UBCs는 1.21 A/cm2에서 0.33 A/cm2로 감소하였다. de-coated Al can granules은 1.09 A/cm2에서 0.54 A/cm2로, construction aluminum materials은 1.20 A/cm2에서 1.01 A/cm2로, yogurt lids은 1.20 A/cm2에서 0.25 A/cm2로, high-purity aluminum은 1.27 A/cm2에서 1.23 A/cm2로 감소했다. high-purity hydrogen (99.999%) 및 기타 여러 종류의 폐알루미늄 수화반응 기반 수소와 비교하여 순환전압전류법(CV)에서 UBCs 및 yogurt lids을 제외하고는 큰 성능 저하가 발생하지 않았다. 본 실험에서 다른 폐알루미늄과 달리 UBCs와 yogurt lids에 코팅된 폴리머는 연료전지의 막전극접합체(MEA)에 직접적인 손상을 주어 내구성에 영향을 주는 것으로 판단된다. 또한 임피던스 분광분석법 (EIS)에서 UBCs와 de-coated Al can granules 기반의 수소들은 높은 임피던스를 가지며 전하 이동에 크게 영향을 받았다. Construction aluminum materials에서 생성된 수소는 99% 이상의 고농도를 가지고 있어 초기 운전 성능은 고농도와 크게 다르지 않았으나, 대부분의 폐알루미늄 수화반응 기반 수소는 PEMFC 운전에 적용했을 때 high-purity hydrogen보다 더 많은 열화를 보였다. 특히, 폴리머 코팅된 폐알루미늄은 열화가 심해 PEMFC에 공급하기 전에 수소가스 농도를 높이기 위한 추가 장치 설치가 필수적이고, 폐알루미늄을 전처리하여 수소를 생산하거나 수소 생산 후 불순물 제거 공정을 거치면 경제적이고 효과적인 연료전지 연료 공급 대안이 될 수 있을 것으로 판단된다.|As global warming becomes more and more severe and abnormal climate events occur frequently, efforts to lower the global average temperature rise are taking place worldwide. As a result, hydrogen is receiving much attention in various fields as a new potential candidate to replace fossil fuels as a future next-generation energy source. It is emerging as the core of carbon-neutral policy. However, about 75% of the world's hydrogen comes from natural gas reforming, generating carbon dioxide, and is a problem. In addition, high production, storage, and transportation costs are also a problem in the existing hydrogen industry. In this study, hydrogen was produced through a waste aluminum hydration reaction and directly supplied to a polymer electrolyte membrane fuel cell (PEMFC) to determine whether it was suitable as a fuel and to confirm the possibility of hydrogen production. The aluminum used in this study is UBCs (used beverage cans, A3104), de-coated aluminum can granules (A3104, A5182), construction aluminum materials (A6063), yogurt lids (A8011), and high-purity aluminum with a purity of 99.99%. To analyze the characteristics of the membrane electrode assembly (MEA) after operating the fuel cell using aluminum hydration reaction-based hydrogen, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were performed. The waste aluminum hydration reaction was performed with 5 g of waste aluminum and 200 ml of 1, 3, and 5 M NaOH aqueous solution. The hydrogen production was 6435, 6630, 6540, 5124, and 6855 mL. The temperature rose to 43, 79, 40, 63, and 63 ℃ respectively, when 5 g of UBCs, de-coated Al can granules, construction aluminum materials, yogurt lids, and high-purity aluminum were added to 5 M NaOH solution. In the 3 M NaOH solution, hydrogen was produced in 6270, 6480, 6540, 4950, and 6710 mL, respectively, and the temperature rose to 38, 76, 37, 55, and 32 ℃. In the application of PEMFC, using conventional high-purity hydrogen (99.999%), the current density at 0.6V was reduced from 1.25 A/cm2 to 1.20 A/cm2 after 200 cycles, UBCs was reduced from 1.21 A/cm2 to 0.33 A/cm2, de-coated Al can granules were reduced from 1.09 A/cm2 to 0.54 A/cm2, construction aluminum materials were reduced from 1.20 A/cm2 to 1.01 A/cm2, yogurt lids were reduced from 1.20 A/cm2 to 0.25 A/cm2, and high-purity aluminum was reduced from 1.27 A/cm2 to 1.23 A/cm2. Compared to high-purity hydrogen (99.999%) and other waste aluminum hydration reaction-based hydrogen, significant performance degradation did not occur in cyclic voltammetry (CV) except UBCs and yogurt lids. Unlike other waste aluminum in this experiment, it is considered that the polymer coating on UBCs and yogurt lids directly damage the fuel cell's membrane electrode assembly (MEA), affecting durability. Also, in electrochemical impedance spectroscopy (EIS), the hydrogen-based on UBCs and de-coated Al can granules have high impedance and are greatly affected by charge transfer. Hydrogen generated from construction aluminum materials had a high concentration of more than 99%, so its initial operating performance was similar to that of a high concentration. However, most waste aluminum hydration reaction-based hydrogen showed more degradation than conventional high-concentration hydrogen when applied to PEMFC operation. Especially, waste aluminum with polymer coating is more degraded, so it is essential to install additional devices to increase the concentration of waste aluminum-based hydrogen gas before supplying it to PEMFC. As a result, if hydrogen production through pretreatments of waste aluminum or a process of removing impurities after hydrogen production is performed, it can be an economical and effective alternative to fuel supply for fuel cells.