Electronic Theses and Dissertation

Hidrogen adalah pembawa energi (energy carrier) terbarukan yang dapat menyimpan atau mengirimkan energi dalam jumlah yang sangat besar. berbagai jenis kenderaan fuel cell berbahan bakar hydrogen sudah mulai dibuat dan dipasarkan. namun salah satu masalah utama terkait dengan penggunaan hidrogen sebagai bahan bakar adalah teknologi penyimpanan hidrogen tersebut. menemukan solusi untuk masalah penyimpanan hidrogen dianggap sebagai tantangan utama bagi ekonomi hidrogen saat ini. kandidat logam yang menjanjikan untuk aplikasi tangki penyimpan hidrogen keadaan padat (solid state hydrogen storage) adalah magnesium karena kapasitas penyerapan hidrogen yang tinggi, kelimpahannya dan harganya yang murah. namun magnesium memiliki kekurangan yaitu kinetika penyerapan hidrogen yang lambat dan suhu penyerapan-desorpsi yang tinggi. upaya perbaikan sifat magnesium telah dilakukan dengan menyisipkan material silica maupun karbon aktif yang bertindak sebagai katalis dalam reaksi penyimpanan dan pelepasan hydrogen oleh magnesium. silica dan karbon aktif yang digunakan umumnya berupa produk industry atau sintetis. tujuan penelitian disertasi ini adalah membuat silica dan karbon aktif berasal dari bahan alam dan mempelajari karakteristik dan potensinya sebagai bahan adisi pada material magnesium. karbon aktif dibuat dari limbah kulit buah kopi jenis robusta gayo berasal dari perkebunan di kabupaten bener meriah, sedangkan silika diekstraksi dari limbah abu terbang batubara rangking rendah di pltu nagan raya. metode yang dilakukan terdiri dari 3 tahapan yaitu tahap pembuatan karbon aktif dari kulit kopi, tahap ekstraksi silika dari abu terbang, dan tahap penyisipan karbon aktif dan silika kedalam magnesium. bagaimana pengaruh parameter proses terhadap karakteristik fisika kimia karbon aktif dan silika yang diperoleh serta potensinya sebagai bahan adisi pada material magnesium dipelajari berdasarkan uji sem/eds, uji xrd, uji bet, uji tga/dsc dan uji ftir. diharapkan diperoleh metode yang tepat untuk menghasilkan sampel karbon aktif dan silica berasal dari bahan alam sekaligus peluang potensinya sebagai katalis pada material penyimpan hidrogen berbasis magnesium. selain itu pemanfaatan kedua jenis limbah berupa kulit kopi dan abu terbang tersebut sebagai bahan baku katalis akan menjadi alternatif baru untuk meningkatkan nilai tambah limbah perkebunan maupun limbah industri sebagai upaya mengurangi pencemaran lingkungan. kata kunci : kulit kopi, abu terbang, karbon aktif, silika, magnesium

Hydrogen is an environmentally friendly renewable energy source that stores enormous amounts of energy. Various types of hydrogen fuel cell vehicles have begun to be made and marketed. However, one of the main problems associated with using hydrogen as a fuel is the hydrogen storage technology. Finding a solution to the hydrogen storage problem is considered a major challenge for today's hydrogen economy. A promising metal candidate for solid state hydrogen storage tank applications is magnesium because of its high hydrogen absorption capacity, abundance and low price. However, magnesium has disadvantages, namely slow hydrogen absorption kinetics and high absorption-desorption temperatures. Efforts to improve the properties of magnesium have been made through reducing the size of magnesium particles using mechanical grinding, or inserting silica, carbon or activated carbon materials which act as catalysts in the reaction to release hydrogen by magnesium. The silica, carbon and activated carbon used are generally industrial or synthetic products. The aim of this dissertation research is to make silica, carbon and activated carbon from natural materials and study their characteristics and potential as adducts (catalysts) in magnesium hydride materials. Carbon and activated carbon are made from Robusta Gayo coffee fruit skin waste from plantations in Bener Meriah district, while silica is extracted from coal fly ash waste at the Nagan Raya PLTU. The method used consists of 3 stages, namely the stage of making carbon and activated carbon from coffee skins, the stage of extracting silica from fly ash, and the stage of inserting carbon, activated carbon and silica into magnesium. How the process parameters influence the physicochemical characteristics of the carbon, activated carbon and silica obtained and their potential as adducts in magnesium materials is studied based on the SEM/EDS test, XRD test, BET test, TGA/DSC test and FTIR test. The results obtained show that the three types of adducts are capable of behaving as catalysts (surface catalysts) in catalytic reactions on MgH2 materials. MgH2 crystals added with carbon and activated carbon from coffee skins and added with silica from coal fly ash were successfully obtained with an average size of close to 10 nm with a 4 hour milling process. In general, the addition of carbon catalysts, activated carbon, and silica has succeeded in reducing the onset temperature of MgH2 and accelerating the kinetics of the MgH2 reaction. Especially the addition of SiO2 catalyst from fly ash to MgH2 and a 4 hour milling process gave quite promising effects. The reduction in crystal size obtained was 9.46 nm and was able to reduce the desorption temperature of pure MgH2, namely at a temperature of 346.59 oC in 8.71 minutes. The use of these two types of waste in the form of coffee husks and fly ash as catalyst raw materials is expected to become a new alternative to increase the added value of plantation waste and industrial waste as an effort to reduce environmental pollution while also participating in the energy transition process towards renewable energy. Key words: Coffee skin, Fly ash, Activated carbon, Silica, Magnesium, Hydrogen