53沼津工業高等専門学校研究報告
第 51 号，2017 年 1 月㖡㟁ᴟࢆ⏝࠸ࡓ஧㓟໬Ⅳ⣲࠿ࡽࡢࢠ㓟⏕ᡂࡢ◊✲஭ୖ㯇*㸪኱ᓥ୍┿*Investigation of CO2 Electrochemical Reduction to Formic Acid on Copper ElectrodeUruha Inoue*, Kazumasa Oshima*
Abstract: Electrochemical reduction of CO2 to formic acid was performed on copper electrode in
1.0M K2CO3 solution. Formic acid has been paid attention as a hydrogen carrier, because it has
high storage capacity (54 kg-H2 m-3) and stability (b.p.=100ºC). Copper electrode was preparedwith an electroless deposition method. From results, iron rod showed high current density,
which was important factor as an electrode substrate. Depositing copper on iron rod increased
current, due to its high surface area, and formic acid was detected after 5 h reaction. FromSEM images before/after reaction, it was found that copper on the electrode substrate wasstable during the reaction.
Key Words:

CO2 reduction, Formic acid, Electrochemical reduction, Cu electrodeࡑࡇ࡛ᮏ◊✲࡛ࡣ㸪㖡㟁ᴟࡢ㧗⾲㠃✚໬࠾ࡼࡧ⾲㠃ᙧ≧ࡢ䠍䠊⥴ ゝไᚚࢆ≺࠸㸪ᇶᯈ㟁ᴟ࡟㖡ࢆᢸᣢࡉࡏࡓ㟁ᴟࢆㄪ〇ࡋ㸪ࡑ㏆ᖺ㸪Ỉ⣲♫఍ࡢᐇ⌧࡟ྥࡅ࡚㸪ࡑࡢ࢟ࣕࣜ࢔࡟㛵ࡍࡿࡢ཯ᛂ≉ᛶࢆホ౯ࡍࡿࡇ࡜ࢆ┠ⓗ࡜ࡍࡿ㸬◊✲ࡀ┒ࢇ࡟⾜ࢃࢀ࡚࠸ࡿ㸬ᾮయỈ⣲㸪࢔ࣥࣔࢽ࢔㸪࣓ࢳࣝࢩࢡࣟ࣊࢟ࢧࣥ࡞࡝ࡢೃ⿵࡟ᣲࡆࡽࢀ࡚࠸ࡿࡀ㸪Ᏻ඲ᛶࡸỗ⏝ᛶࡢ㧗ࡉ࠿ࡽࢠ㓟࡟ὀ┠ࡀ㞟ࡲࡗ࡚࠸ࡿ㸬ࢠ㓟ࡣỈ⣲㈓ⶶᐦᗘ 54 kg-H2 m-3 ࢆ᭷ࡋ㸪࣓ࢳࣝࢩࢡࣟ࣊࢟ࢧࣥࡢ䠎䠊ᐇ㦂᧯స㸰㸬㸯 㟁ᴟࡢㄪ〇47 kg-H2 m-3 ࡟༉ᩛࡍࡿ㸬ࡲࡓἛⅬࡀ⣙ 100ºC ࡛࠶ࡿࡇ࡜ᇶᯈ࡜࡞ࡿ㟁ᴟ࡟ࡣⅣ⣲࣭ࢽࢵࢣ࣭ࣝ㖡࣭ள㖄࣭┿㘷࣭࠿ࡽ㸪࢔ࣥࣔࢽ࢔(–33.4ºC)ࡸᾮయỈ⣲(–253ºC)ࡼࡾࡶᏳ඲

ࢪ࣑ࣗࣛࣝࣥ(ྛ 4 mmI)࣭㕲(5 mmI)ࢆ⏝࠸ࡓ㸬ࡲࡓᇶᯈᛶ࣭ỗ⏝ᛶ࡟ඃࢀ࡚࠸ࡿ㸬ࡲࡓࢠ㓟⏕ᡂࡢཎᩱࡣ஧㓟໬Ⅳ㟁ᴟ࡬ࡢ㖡ᢸᣢ࡟ࡣḟ࡟♧ࡍ↓㟁ゎࡵࡗࡁἲࢆ⏝࠸ࡓ㸬࢖⣲࡛࠶ࡾ㸪ᕤᴗⓗ࡟୙せ࡞ࡶࡢࢆ෌฼⏝࡛ࡁࡿⅬ࡛ࡶὀ┠࢜ࣥ஺᥮Ỉ࡟◪㓟㖡(III)࣭୕Ỉ࿴≀㸪Ⅳ㓟ࢼࢺ࣒ࣜ࢘㸪㓇ࡉࢀ࡚࠸ࡿ㸬

▼㓟ࢼࢺ࣒࣒ࣜ࢘࢝ࣜ࢘㸪Ỉ㓟໬ࢼࢺ࣒ࣜ࢘ࢆ⁐ゎࡉࡏ㸪஧㓟໬Ⅳ⣲࠿ࡽࡢࢠ㓟⏕ᡂ཯ᛂࢆᘧ 1 ࡟♧ࡍ㸬ᇶᯈ㟁ᴟࢆ 4 cm ᾐₕࡉࡏࡿ㸬ࡑࡇ࡟࣒࣍ࣝ࢔ࣝࢹࣄࢻࢆ   CO2 + H2 Ѝ HCOOH    ῧຍࡉࡏࡿࡇ࡜࡛◪㓟㖡ࢆ㑏ඖࡋ㸪㖡ࢆᇶᯈ㟁ᴟ࡟ᯒฟࡉ

'H 0298 = –31.3 kJ mol-1  ᘧ 1ࡏࡿ㸬ᮏᡭἲ࡟ࡼࡾᯒฟࡉࡏࡓ㖡㟁ᴟࡣ㸪10 mg cm-2 ࡛࠶஧㓟໬Ⅳ⣲࠿ࡽࡢࢠ㓟⏕ᡂࡣ୺࡟㘒యゐ፹ࢆ⏝࠸ࡓᾮ┦ࡾ㸪⾲㠃≧ែࡣ SEM(㉮ᰝᆺ㟁Ꮚ㢧ᚤ㙾)࡟ࡼࡗ࡚ほ ࣭ホ཯ᛂ࡛⾜ࢃࢀ࡚࠸ࡿ㸬Himeda ࡽࡣ Ir 㘒యࢆ⏝࠸࡚஧㓟໬౯ࡋࡓ㸬Ⅳ⣲࡜Ỉ⣲࠿ࡽ㧗ຠ⋡࡞ࢠ㓟⏕ᡂࢆሗ࿌ࡋ࡚࠸ࡿ[1]㸬୍᪉࡛ཎᩱ࡟Ỉ⣲ࢆ⏝࠸࡚࠸ࡿⅬࡸ㸪㧗౯࡞㘒యゐ፹ࢆ⏝࠸࡚㸰㸬㸰 ࢠ㓟⏕ᡂホ౯ヨ㦂࠸ࡿࡇ࡜࠿ࡽ㸪ࡼࡾᏳ౯࡞ࣉࣟࢭࢫࡢ㛤Ⓨࡀᮃࡲࢀ࡚࠸ࡿ㸬 㟁ᴟୖ࡛ࡢࢠ㓟⏕ᡂ཯ᛂࡣ㸪ᅗ 1 ࡟♧ࡍ⿦⨨ࢆ⏝࠸࡚ホࡑࡇ࡛ᮏ◊✲࡛ࡣᏳ౯࡞㖡࡟╔┠ࡋ㸪ỗ⏝ᛶࡢ㧗࠸Ỉࢆཎ౯ࡋࡓ㸬స⏝ᴟ࡟㔠ᒓᲬ㸪ᑐᴟ࡟Ⅳ⣲Წࢆタ⨨ࡋ㸪┤ὶ㟁ᩱ࡜ࡋࡓ㟁Ẽ໬Ꮫ཯ᛂ࡟ࡼࡿࢠ㓟⏕ᡂࢆヨࡳࡿ㸬Hara ࡽᅽࢆ༳ຍࡋࡓ㸬㟁ゎᾮ࡟ࡣ 1.0M K2CO3 Ỉ⁐ᾮࢆ⏝࠸࡚㸪ࡣ✀ࠎࡢ㟁ᴟୖ࡛ࡢࢠ㓟⏕ᡂࢆヨࡳ㸪㖡ࡀࢠ㓟⏕ᡂࡢ㑅ᢥ஧㓟໬Ⅳ⣲ࢆࣂࣈࣜࣥࢢ࡟ࡼࡾ౪⤥ࡋ㟁Ẽ໬Ꮫ཯ᛂࢆ⾜ᛶࡀ㧗࠸ࡇ࡜ࢆሗ࿌ࡋ࡚࠸ࡿ[2]㸬୍᪉࡛཯ᛂ⋡ࡀஈࡋࡃ㸪ࡗࡓ㸬཯ᛂ୰ࡣ㟁ὶ್࠿ࡽ཯ᛂ⋡ࢆホ౯ࡋ㸪ࢠ㓟⏕ᡂࡣ 5ࡼࡾ཯ᛂᛶࡢ㧗࠸㟁ᴟࡢ㛤Ⓨࡀᮃࡲࢀ࡚࠸ࡿ㸬᫬㛫ࡢ཯ᛂᚋࡢ⁐ᾮࢆ GC-TCD ࡟ࡼࡾホ౯ࡋࡓ㸬ࡲࡓ㟁Ẽ໬Ꮫ཯ᛂࡢホ౯࡜ࡋ࡚࣎ࣝࢱ࣓ࣥࢺ࣮ࣜࢆᐇ᪋ࡋࡓ㸬㉮*≀㉁ᕤᏛ⛉ᰝ㏿ᗘࢆ 10 mV sec-1 ࡜ࡋ㸪0 V ࠿ࡽ–4.0 V ࡲ࡛ኚ໬ࡉࡏ

Department of Chemistry and Biochemistryࡓ㸬54

沼津工業高等専門学校研究報告

第 51 号

CO2ൕԢ઴ൕԢ‫ޛ‬10 mg cm-2 10 mg cm-2ൕԢ઴ൕԢ‫ޛ‬

ᅗ 3 ཯ᛂ๓ᚋࡢ㟁ᴟࡢ෗┿࣭SEM ീᅗ  ࢠ㓟⏕ᡂホ౯ヨ㦂ࡢ཯ᛂ⿦⨨ᅗ㸱㸬㸰 㖡ᢸᣢ㕲㟁ᴟࡢホ౯཯ᛂ๓ᚋࡢ SEM ീ࠾ࡼࡧ EDS ࣐ࢵࣆࣥࢢࢆᅗ 3 ࡟♧䠏䠊⤖ᯝ䛚䜘䜃⪃ᐹࡍ㸬㖡ࡢ⾲㠃ᙧ≧ࡣኚ໬ࡋ࡚࠸ࡿࡶࡢࡢ㸪ᇶᯈ࡛࠶ࡿ㕲ࡢ㸱㸬㸯 ࢠ㓟⏕ᡂホ౯ヨ㦂㟢ฟࡣほ ࡉࢀ࡚࠾ࡽࡎ㸪ࡲࡓ཯ᛂᚋࡢᢸᣢ㔞ࡶ 10 mg ࡲࡎ–2.5 V ༳ຍ᮲௳࡛ࡢᇶᯈ㟁ᴟࡢホ౯ࢆᐇ᪋ࡋࡓ㸬ᮏ

cm-2 ࡛࠶ࡗࡓࡇ࡜࠿ࡽ㸪Ᏻᐃࡋࡓ㖡ᢸᣢࡀ☜ㄆࡉࢀࡓ㸬࡞㟁ᅽࡣ Hara ࡽࡢᐇ㦂[2]ࢆཧ⪃࡟ࡋ㸪㟁ὶኚ໬࠿ࡽᇶᯈ㟁࠾⾲㠃ᙧ≧ࡢኚ໬ࡣ㸪㟁Ẽ໬Ꮫ཯ᛂ࡟ࡼࡾ㖡ࡢ୍㒊ࡀ㓟໬ᴟ࡜ࡋ࡚ࡢᛶ⬟ࢆホ౯ࡋࡓ㸬✀ࠎࡢᇶᯈ㟁ᴟࢆヨ㦂ࡋࡓ⤖ࡉࢀࡓࡓࡵ࡟㉳ࡇࡗࡓ࡜⪃࠼ࡽࢀࡿ㸬ᐇ㝿࡟཯ᛂᚋࡢ෗┿ᯝ㸪㕲ࡀ᭱ࡶᏳᐃࡋࡓ㟁ὶࢆ♧ࡋ࡚࠾ࡾ㸪11 mA cm-2 ࢆ♧࠿ࡽࡶ㔠ᒓ㖡≉᭷ࡢගἑࡀኻࢃࢀ࡚࠸ࡿࡇ࡜ࡀࢃ࠿ࡿ㸬ࡋࡓ㸬௚ࡢ㟁ᴟࢆ⏝࠸ࡓሙྜࡣ㸪㟁ὶࡀᑠࡉ࠸ࡶࡋࡃࡣ⤒ ࡑࡋ࡚㟁ᴟࡢホ౯࡜ࡋ࡚㕲㟁ᴟ࠾ࡼࡧ㖡ᢸᣢ㕲㟁ᴟࡢ᫬ⓗ࡞పୗࡀほ ࡉࢀ㸪㟁ゎᾮ୰࡛㟁ᴟ⾲㠃࡟㓟໬⿕⭷ࡀ࣎ࣝࢱ࣓ࣥࢺ࣮ࣜࢆ⾜ࡗࡓ㸬ࡑࡢ⤖ᯝࢆᅗ 4 ࡟♧ࡍ㸬࠸ࡎᙧᡂࡉࢀ࡚࠸ࡿࡇ࡜ࡀ♧၀ࡉࢀࡓ㸬ࢀࡢ㟁ᴟ࡟࠾࠸࡚ࡶ㸪–2.1 V ࠿ࡽ㟁ὶ್ࡢቑ኱ࡀぢࡽࢀࡿ ḟ࡟Ᏻᐃࡋࡓ㟁ὶࡀὶࢀࡓ㕲࠾ࡼࡧ㸪ཧ↷⏝ࡢ┿㘷ࢆᇶࡇ࡜࠿ࡽ㸪ᮏ཯ᛂࡣ–2.1 V ௨ୖ࡛㐍⾜ࡍࡿࡇ࡜ࡀࢃ࠿ࡗࡓ㸬ᯈ㟁ᴟ࡜ࡋ࡚㸪㖡ᢸᣢ࡟ࡼࡿࢠ㓟⏕ᡂࢆホ౯ࡋࡓ㸬ࡑࡢ⤖㟁ὶ㟁ᅽ᭤⥺࡟኱ࡁ࡞┦㐪ࡣ࡞࠸ࡶࡢࡢ㸪㖡ᢸᣢࢆࡍࡿࡇ

ᯝࢆᅗ 2 ࡟♧ࡍ㸬࠸ࡎࢀࡢᇶᯈ㟁ᴟ࡟࠾࠸࡚ࡶ㖡ࢆᢸᣢࡍ࡜࡛㟁ὶࡢቑ኱ࡀほ ࡉࢀ࡚࠾ࡾ㸪ᐃᖖヨ㦂ࡢ⤖ᯝ࡜ྠᵝࡿࡇ࡜࡛㟁ὶ್ࡢቑ኱ࡀほ ࡉࢀࡓ㸬ࡇࢀࡣ㖡ᢸᣢ࡟ࡼࡿ࡟㸪⾲㠃✚ቑ኱࡟ࡼࡿ㟁ὶቑ኱ࡀ♧၀ࡉࢀࡓ㸬㟁ᴟ⾲㠃✚ࡢቑ኱࡟ࡼࡿࡶࡢ࡜⪃࠼ࡽࢀࡿ㸬ࡲࡓ㕲࡟㖡ࢆ௨ୖࡢ⤖ᯝࡼࡾ㸪஧㓟໬Ⅳ⣲࠿ࡽࡢ㟁Ẽ໬Ꮫ཯ᛂ࡟ࡼࡿ

ᢸᣢࡉࡏࡓ㟁ᴟ࡟ࡢࡳࢠ㓟ࡢ⏕ᡂࡀ☜ㄆࡉࢀࡓ㸬ࡇࡢࡇ࡜ࢠ㓟⏕ᡂ࡟ࡣ㸪㕲ࢆᇶᯈ㟁ᴟ࡜ࡋࡓ㖡㟁ᴟࡀ㐺ࡋ࡚࠸ࡿࡇ

࠿ࡽ㕲ࢆᇶᯈ㟁ᴟ࡜ࡋ࡚㸪⾲㠃࡟㧗⾲㠃✚࡞㖡ࢆᢸᣢࡉࡏ

࡜ࡀࢃ࠿ࡗࡓ㸬ࡿࡇ࡜࡛ࠊ㟁Ẽ໬Ꮫ཯ᛂ࡟ࡼࡗ࡚ࢠ㓟ࡀ⏕ᡂࡍࡿࡇ࡜ࡀࢃ
0࠿ࡗࡓ㸬
50

Current / mA

40

30

Cu rodBrass rod
Fe rod20

Blank : Bare rod
Filled : Cu plating100Current / mA-100

Fe rod-200

0-300-40-400-500

Cu/Fe rod -80-3-4-3-2.5-2

Voltage / V-2-1-1.50ᅗ 4 㕲ᇶᯈ㟁ᴟࡢ࣎ࣝࢱ࣓ࣥࢺ࣮ࣜヨ㦂⤖ᯝ
050

100

150

200250Time on stream / min300

ᅗ 2 ྛ㟁ᴟࢆ⏝࠸ࡓࢠ㓟⏕ᡂヨ㦂ࡢ⤖ᯝ[1] Y. Himeda et al.: Nature Chemistry, 4 (2012) 383.
[2] K. Hara et al.: J. Electroana. Chem., 391 (1995) 141.