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re: [fw] Fuel cell

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  • Ihsan Hariadi by way of Mujaya Hertadi
    ... Apakah ada yang dapat menceritakan prinsip sistim fuel cell ini. Dimana letak kesulitan pembuatan fuel cell dan apakah benar bisa menyaingi motor bakar
    Message 1 of 1 , Dec 1, 2000
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      Elwin RACHMAT :
      -------------
      Apakah ada yang dapat menceritakan prinsip sistim fuel cell ini.
      Dimana letak kesulitan pembuatan fuel cell dan apakah benar bisa
      menyaingi motor bakar secara ekonomis.

      Kira-kira bagaimana bahan bakar hidrogen dapat diproduksi
      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
      secara ekonomis (dari gas alam ?).
      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

      ihsan:
      -----
      terimakasih atas kiriman artikel tutorial mengenai Sel bahan
      bakar yang ditulis sangat sistematik oleh mas Basuki Suhardiman
      (mudah-mudahan sudah ada website Sel Bakar berbahasa Indonesia? ).

      Saya tidak tahu banyak mengenai topik ini, tetapi menjawab
      bagian pertanayaan mas Elwin rachmat yang saya garis bawahi di atas:
      dapat saya sampaikan jawabn singkat :

      (*) benar, saat ini cara memproduksi hidrogen secara ekonomis
      (dan kemudian cara "menyimpan" hidrogen tsb. secara padat
      dan rapi, masih menjadi persoalan nampaknya).

      (*) Sekitar 3 bulan yang lalu ada pameran kecil tentang sumber
      energi "berkelanjutan" di kabupaten Duisburg, salah satu
      topiknya tentu saja Sel BahanBakar. Sudah ada produk komersial
      Sel bahan bakar untuk aplikasi Rumah Tangga (household),
      di mana bahan bakar hidrogennya dihasilkan dari proses
      "cracking" gas alam (hidrokarbon) yang tentu mengandung
      C dan H. Dari sini akan dihasilkan H2, tapi juga akan
      dihasilkan CO2. Meskipun demikian, tetap dinilai lebih
      ramah lingkungan. Hidrokarbon merupakan salah satu
      alternatif bahan baka tak langsung, seperti yang tercantum
      dalam tabel yang dibuat mas Basuki di bawah ini.

      basuki:
      -----

      > ---------------------------
      > Sel Bahan Bakar (Fuel Cell)
      > ---------------------------
      >
      >
      > 1. Deskripsi Umum
      > 2. Sifat Sifat Sel Bahan Bakar Secara Umum
      > 4. Komponen Komponen Dasar Sel Bahan Bakar
      > 5. Karakteristik Karakteristik Umum Unjuk Kerja Sel Bahan Bakar
      > 6. Klasifikasi Sistem Sel Bahan Bakar
      >
      > ...............

      ihsan:
      -----
      tabel dari mas basuki (saya tulis kembali, pls correct me ... )

      -----------------------------------------------------------------------
      Bahan Bakar Oksidan Suhu Elektrolit
      -----------------------------------------------------------------------
      Langsung Tak Langsung
      -----------------------------------------------------------------------
      Hidrogen Hydride Oksigen Rendah LarutanAs. Sulfat
      Hydrazine Ammonia Oksigen (udara) Menengah
      Ammonia Hydrocarbon Hidrogen peroks Fosforik
      Hydrocarbon Methanol Tinggi SPE
      Methanol Ethanol Larutan Basa
      Gas Batubara Batubara Molten Alkaline Larutan Karbonat
      Molten Carbonate Solid Oxide
      -------------------------------------------------------------------------

      catatan:
      --------
      suhu rendah : 120 derajat celcius
      suhu menengah : 120 - 160 derajat celcius
      suhu tinggi : 260 - 750 derajat celcius
      SPE : Solid Polymer Electrolyte

      Nah, para pecinta lingkungan mungkin akan concern jika melihat
      bahwa Sel Bahan Bakar nya sendiri operasinya sangat ramah lingkungan,
      tetapi jika bahan bakar hidrogennya dihasilkan menggunakan energi
      yang sumbernya tak terbarukan (misalnya menggunakan listrik PLN,
      yach, ... mungkin jadi sami mawon .. ;-) ).

      Salah satu alternatif menhatasi hal ini, adalah menggunakan
      listrik berasal dari sel surya (sel photovoltaic) seperti
      disebutkan pada artikel di bawah ini.

      {
      Sedikit pertanyaan dari membaca artikel di bawah ini :
      apakah betul untuk proses elektrolisa air menjadi H2 dan O2
      itu ada nilai "optimum" untuk tegangan DC yang digunakan, yaitu
      1.23 volt? emangnya apa sih yang terjadi jika digunakan nilai
      tegangan yang lebih tinggi dari itu? apakah efisiensi juga?
      bagian yang mengandung informasi mengenai nilai tegangan optimum
      ini saya "stabilo" di bawah. Kliatan nggak warna stabilonya dari
      sana? ... ;-) ). Selamat menyimak ...

      } -ihsan-


      -------------------------------------------------
      From : Danial Irfachsyad <ac.uk>
      To : fisika_indonesia@egroups.com
      Date : Tue Sep 19, 2000 5:58pm
      Subject: Device ups hydrogen energy from sunlight
      -------------------------------------------------

      Science News, Vol. 158, No. 12, Sept. 16, 2000, p. 182.


      -----------------------------------------
      Device ups hydrogen energy from sunlight
      -----------------------------------------

      -= Peter Weiss =-

      Here's a recipe for a cleaner, healthier planet: Take some water,
      add solar energy, extract hydrogen, and use it to power fuel
      cells for running cars and other machines. Then, collect their
      water emissions and start the procedure again.

      One look at the list of ingredients in today's fuel cells,
      however, shows that this ideal isn't yet being followed. Because
      processes that use sunlight to extract hydrogen remain costly and
      inefficient, fossil fuels still supply the hydrogen in most fuel
      cells.

      Hoping to break the fossil fuel habit, a team of Israeli, German,
      and Japanese scientists has created a device that boosts the
      efficiency of solar-powered hydrogen extraction by 50 percent.

      *****************************************************************
      The group placed a photovoltaic cell on top of two flat, finger-
      long electrodes. The combination "is very efficient in converting
      solar energy [into an electric current] but also provides nearly
      the ideal voltage for splitting water" into hydrogen and oxygen,
      says team leader Stuart Licht of the Technion in Haifa, Israel. A
      water molecule splits, or undergoes electrolysis, at only 1.23
      volts.
      *****************************************************************

      Licht and his colleagues describe their device in the Sept. 14
      Journal of Physical Chemistry B. The gadget converts sunlight to
      an electrolysis current with 18.3 percent efficiency. In turn,
      the current creates hydrogen gas as it passes through acidic
      water.

      The device is "showing the pathway towards higher efficiencies
      for direct solar-to-hydrogen production," comments John A. Turner
      of the National Renewable Energy Laboratory (NREL) in Golden,
      Colo. The newly achieved efficiency may already be high enough
      for commercial hydrogen generators to be feasible. "That still
      needs to be figured out," Turner says.

      In 1998, he and Oscar Khaselev, then also of NREL, demonstrated a
      novel apparatus for solar-to-hydrogen conversion (SN: 4/18/98, p.
      246). To achieve unprecedented efficiency, the device used
      multiple layers of semiconductor materials. The researchers
      arranged the layers to form two active regions, or junctions,
      that would absorb solar photons that dislodge electrons. Some of
      the less energetic photons weren't captured in the first junction
      but passed to the second, where they generated more current.

      The design gained an energy advantage by combining solar
      electricity and water splitting into one unit. Their cell's 12.4
      percent efficiency-nearly twice that of any previous solar-to-
      hydrogen device-has held as the record until now.

      Licht and his colleagues have improved upon that pioneering
      effort in several crucial ways. In one sense, the NREL device was
      all wet: It had to be completely immersed in water to operate.
      That feature forced the researchers to select semiconductors that
      wouldn't break down in solution.

      By keeping their stack of semiconductor layers high and dry,
      Licht and his group were free to optimize them for both
      converting sunlight to electricity and water splitting. Their
      design permits a low electrolysis current, which also reduces
      energy waste.

      Licht and his coworkers say that besides besting the solar-to-
      hydrogen conversion record, their work opens the way to
      efficiencies not considered possible before. Using measured
      photoelectric efficiencies of seven semiconductor combinations
      not yet tested in hydrogen generation, they predict maximum
      solar-to-hydrogen conversion efficiencies of up to 31 percent.

      Thermodynamics theory says the maximum could range above 40
      percent for a two-junction converter, but no one has previously
      predicted better than 24 percent performance for practical
      devices, Turner says. Experimentally achieving the new
      prediction "would be an accomplishment indeed!" he adds.

      ----------
      References:
      ----------
      Licht, S., et al. 2000. Efficient solar water splitting,
      exemplified by RuO2-catalyzed AlGaAs/Si photoelectrolysis.
      Journal of Physical Chemistry B. 104(Sept 28):8920

      Further Readings:

      Perkins, S. 1997. Electric cars...fueled by gasoline?
      Science News 152(Nov. 1):279.

      Wu, C. 1999. Catalysts make hydrogen under the hood.
      Science News 155(May 15):314.

      ______. 1998. Quick screening yields better catalysts.
      Science News 153(June 13):373.

      ______. 1998. Solar cell converts water into hydrogen.
      Science News 153(April 18):246.

      -------
      Sources:
      -------
      1. Stuart Licht
      Technion-Israel Institute of Technology
      Department of Chemistry
      Technion City, Haifa 32000
      Israel

      2. John A. Turner
      MS 1613
      National Renewable Energy Laboratory
      1617 Cole Boulevard
      Golden, CO 80401-3393

      ---= oOo =---
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