Publication: The effect of oxidation atmosphere on morphology and hydrogen productıon efficiency of hematite photo anode produced by oxidation of deposited fe film
Abstract
Hematit, ucuz olması, tabiatta yaygın olarak bulunması, güneş ışınlarının büyük bir kısmını sönümlemesi, 2.0 eV band gap ile en ideal band aralığına sahip olması ve sulu ortamda en kararlı demir oksit olmasından dolayı fotoelektrot üretiminde dikkat çekmektedir. Hematitin %16,8’ lik teorik verimi ile ilgi çekmesine rağmen güneş ışığını hidrojene dönüştürme verimi teorik verimin çok altında kalmıştır. Bunun en önemli nedenleri, Fe2O3’in düşük elektron iletkenliği, düşük boşluk difüzyon mesafesi ve yüksek aşırı gerilim ihtiyacı olarak gösterilmiştir. Bu çalışmada, FTO (Flor katkılı kalay oksit) substratı üzerine elektrokimyasal yöntemle biriktirilen Fe, kontrollü atmosferde termal oksidasyonla başarılı bir şekilde hematite dönüştürülmüştür. Katkısız hematit fotoanotların fotoakım değerleri, oksidasyon ortamı (hava, argon, azot, su buharı+argon), oksidasyon sıcaklığı ve oksidasyon süresi gibi termal oksidasyon parametreleri optimize edilerek geliştirilmiştir. Hazırlanan elektrotların fotoelektrokimyasal testleri üç elektrotlu bir sistemde gerçekleştirilmiştir. Numunelerin fotoakımları, LSV, Mott Schottky ve EIS analizleri kullanılarak karakterize edilmiştir. Oksidasyon ortamı incelendiğinde, su buharı+argon karışımında termal oksidasyonla üretilen fotoanotların PEC (fotoelektrokimyasal) performansının düştüğü, düşük oksijen seviyesine sahip atmosferde üretilen hematit foto-anotların ise PEC performansının arttığı tespit edilmiştir. Filmlerin yüzeyinde oluşan fazların kompozisyonunun tespiti için Raman spektroskopisi ve numunelerin bant aralığının belirlenmesi için UV-vis spektroskopi de yapılmıştır. Numunelerin morfolojileri, taramalı elektron mikroskobu (SEM) kullanılarak karakterize edildi.
Hematite has received attention in photoelectrodes production due to its being cheap, widely available in nature, absorbing most of the sunlight, having the ideal band gap of 2.0 eV, and being the most stable iron oxide in an aqueous environment. Although hematite has attracted attention with its theoretical efficiency of 16,8%, the efficiency of converting sunlight to hydrogen remained well below the theoretical performance. The most important reasons for this are attributed to the low electron conductivity of Fe2O3, low gap diffusion distance and high overvoltage requirement. In this study, Fe deposited on the FTO (Fluorine tin oxide) substrate by the electrochemical path was successfully transformed to hematite by thermal oxidation in a controlled atmosphere. Photocurrent values of undoped hematite photoanodes were developed by optimizing thermal oxidation parameters such as annealing environment (air, argon, nitrogen, water vapor+argon), temperature and exposure time. Photoelectrochemical analyses of the hematite photoanode were carried out in a three-electrode system. Photocurrents of the samples were characterized using LSV, Mott Schottky and EIS analyses. When the effect of the oxidation ambience was investigated, it was observed that the PEC (photoelectrochemical) performance of photoanodes fabricated by thermal oxidation in water vapour decreased. In contrast, the photoelectrochemical achievement of Fe2O3 photoanodes produced in an atmosphere including low oxygen levels increased. Raman spectroscopy determined the composition of phase occurring on the surface of the films and UV-Vis spectroscopy for band gap of samples determination was also performed. Morphologies of hematite thin films were characterised using scanning electron microscopy (SEM).
Hematite has received attention in photoelectrodes production due to its being cheap, widely available in nature, absorbing most of the sunlight, having the ideal band gap of 2.0 eV, and being the most stable iron oxide in an aqueous environment. Although hematite has attracted attention with its theoretical efficiency of 16,8%, the efficiency of converting sunlight to hydrogen remained well below the theoretical performance. The most important reasons for this are attributed to the low electron conductivity of Fe2O3, low gap diffusion distance and high overvoltage requirement. In this study, Fe deposited on the FTO (Fluorine tin oxide) substrate by the electrochemical path was successfully transformed to hematite by thermal oxidation in a controlled atmosphere. Photocurrent values of undoped hematite photoanodes were developed by optimizing thermal oxidation parameters such as annealing environment (air, argon, nitrogen, water vapor+argon), temperature and exposure time. Photoelectrochemical analyses of the hematite photoanode were carried out in a three-electrode system. Photocurrents of the samples were characterized using LSV, Mott Schottky and EIS analyses. When the effect of the oxidation ambience was investigated, it was observed that the PEC (photoelectrochemical) performance of photoanodes fabricated by thermal oxidation in water vapour decreased. In contrast, the photoelectrochemical achievement of Fe2O3 photoanodes produced in an atmosphere including low oxygen levels increased. Raman spectroscopy determined the composition of phase occurring on the surface of the films and UV-Vis spectroscopy for band gap of samples determination was also performed. Morphologies of hematite thin films were characterised using scanning electron microscopy (SEM).