KAJIAN TEORITIS QM/MM MD PENGARUH LARUTAN NaCl PADA TRANSPOR PROTON NAFION DALAM DIRECT METHANOL FUEL CELL (DMFC)

Abstract

. Telah dilakukan penentuan pengaruh penambahan larutan NaCl pada transpor proton nafion dalam Direct Methanol Fuel Cell (DMFC) menggunakan metode QM/MM MD. Pengajian meliputi 4 model transpor proton, yaitu:1. H₃O⁺-H₂O-H₂O(QA);2. H₃O⁺-CH₃OH-H₂O(QB);3. H₃O⁺-Nafion-H₂O  (QC0); dan H₃O⁺-Nafion-H₂O+NaCl_(aq)(QC1). Hasilnya menunjukkan bahwa model QC1 berpengaruh terhadap mekanisme trasnpor proton dengan menurunkan suhu simulasi dibandingkan tiga model transpor proton lain, utamanya model QC0. Model QC1 mempunyai suhu simulasi <500 K sementara QC0 <550 K. Suhu yang tidak terlalu tinggi menjaga sistem dapat berkerja optimum (efisien). Pembentukan transpor proton pada model QC1 merupakan yang tercepat, yaitu melibatkan 2 tahapan proses. Transpor proton I yang melibatkan perpindahan proton dari H₃O⁺ menuju nafion berlangsung selama 81 step (0,81 fs), dan transpor proton II yang melibatkan perpindahan proton dari nafion menuju H₂O berlangsung hanya 11 step (0,11 fs). Transpor proton I model QA memiliki ΔH terendah (0,00653427x10⁴ kj/mol) sementara itu model QC1 nilai ΔH-nya tertinggi (0,016318637x10⁴ kj/mol). Namun nilai ΔH yang tinggi pada model QC1 dapat teratasi dengan hadirnya gugus fungsi -SO₃H dan anion Cl^‑ yang dapat menarik proton lebih cepat dibanding gugus fungsi penarik proton 3 model yang lain. Cepatnya transpor proton dan terjadinya 2 transpor proton sekaligus menyebabkab nilai konduktivitas proton molekul jembatan nafion pada model QC1 adalah yang tertinggi yaitu 5,215941x10⁷ S/cm. Nilai konduktivitas proton tertinggi pada nafion tersebut membuktikan bahwa penambahan larutan NaCl dapat meningkatkan transpor proton dalam sistem transpor proton DMFC.

Kata kunci : QM/MM MD, DMFC, transpor proton, konduktivitas proton, nafion, mekanisme hopping

Abstract. Theoretical studies have been done to determine the effect of adding NaCl to nafion proton transport in Direct Methanol Fuel Cell (DMFC) using QM/ MM MD.  Created 4 proton transport models including of: 1. H₃O⁺-H₂O-H₂O(QA);2. H₃O⁺-CH₃OH-H₂O(QB);3. H₃O⁺-Nafion-H₂O  (QC0); and H₃O⁺-Nafion-H₂O+NaCl_(aq)(QC1). Based on the result of theoretical study that has been done, the model QC1 which nafion proton transport model with the addition of NaCl solution has some effect on the mechanisms of proton transport, such as able to lower the temperature of the simulation compared to other proton transport models especially for QC0 models. QC1 model has <500 K while <550 K simulation temperature. The simulation temperature is not too high, it is expected to maintain the system can work efficiently. Furthermore the formation of QC1 proton transport I is the fastest models for step 81 (0.81 fs), and QC1 is the only model that does proton transport II, it just for 11 step ( 0.11 fs). In proton transport I QA model has the lowest of ΔH (0,00653427x10⁴ kj/mol) meanwhile QC1 model has highest value of ΔH (0,016318637x10⁴ kj/mol). But the value of ΔH is high on QC1 models can be solved with the presence of -SO₃H functional groups and the Cl^- anion can binding proton faster than the functional groups the other models. With the quick proton transport and the two of proton transport at the same time the value of proton conductivity through bridge molecules that is nafion model is the highest 5,215941x10⁷ S/cm. The

highest proton conductivity value on nafion can prove that the addition of NaCl solution can improve proton transport in proton transport system of DMFC. 

Key words : QM/MM MD, DMFC, proton transport, poton conductivity, nafion, hopping mechanism