Enhanced photoelectrocatalytic water oxidation using CoPi modified GaN/MWCNTs composite photoanodes. (15th January 2019)

• Record Type: Journal Article
• Authors: Patil, Santosh S.; Johar, Muhammad A.; Hassan, Mostafa A.; Patil, Deepak R.; Ryu, Sang-Wan
• Is Part Of: Solar energy. Volume 178(2019)
• Page Start: 125
• Page End: 132
• Publication Date: 2019-01-15
• Subjects: GaN -- CoPi co-catalysts -- Multiwall carbon nanotube -- Composite; Solar energy -- Periodicals; Solar engines -- Periodicals; 621.47
• DOI: 10.1016/j.solener.2018.12.028
• Languages: English
• ISSNs: 0038-092X

Abstract

Graphical abstract: Highlights: Combining GaN with MWCNTs improves the light harvesting capability. Large amount of MWCNTs negatively affected PEC performance. The GaN/MWCNTs/CoPi composite photoanode promises unassisted water splitting. The PEC activity was improved, approximately 2.51 times higher compare to bare GaN. Abstract: GaN is promising material for photoelectrochemical (PEC) water oxidation owing to its adjustable band gap and suitable band edge locations, which straddle the H + /H2 and O2 /H2 O redox conditions. However, due to its wide band gap and unavoidable surface defects, the PEC conversion efficiency of GaN is insufficient to be used for practical applications. To improve the PEC efficiency of GaN, we report fabrication of a cobalt phosphate (CoPi)-modified GaN/multiwall carbon nanotube (MWCNT) composite photoanode through combination of metal organic chemical vapor deposition, dip and dry methods, and electrodeposition. Here, GaN photoanodes with different MWCNT surface coverages were obtained by cost effective 'dip and dry' method. Different deposition cycles were performed to prepare a series of samples, which were evaluated for their photoelectrochemical water oxidation. The highest photocurrent density ( J ph ) of 2.23 mA/cm 2 at (0 V vs. Pt electrode) was achieved in a sample with moderate incorporation of MWCNTs, formed by through three cycles of the dip and dry coating (i.e., GaN/MWCNT 3T). We attribute this result to the MWCNTs facilitating light sensitization. However, excessive MWCNT loading produced a shielding effect, which lowered the photocurrent density, and an undesirable two-plateau photocurrent behavior indicating sluggish reaction kinetics. The maximum photocurrent density J ph of 2.81 mA/cm 2, (vs. Pt electrode) with solar to hydrogen conversion efficiency 0.91% was achieved for GaN/MWCNTs 3T/CoPi ternary composite photoanode, which was approximately 2.51 and 1.26 times as high as that of bare GaN and GaN/MWCNTs 3T photoanodes.