The Effect Of Metal Boride Co-catalysts On The Performance Of Ta₃N₅ Photoanodes For Photoelectrochemical Water Splitting

Storing abundant solar energy in chemical form such as hydrogen by photoelectrochemical (PEC) water splitting cells is considered as an effective solution to the energy shortage and environmental pollution issues. The central part of a PEC cell is a semiconductor-based photoelectrode with the main function of absorbing solar light. Modifying the photoelectrode with suiitable co-catalysts can effectively promote the separation of photo-excited charge carriers and lower the reaction kinetic barrier of water splitting reaction. As a consequence, the efficiency of PEC water splitting can be greatly improved. Therefore, it is highly desirable to develop highly efficient co-catalysts in order to obtain efficient PEC cells.In this thesis, we explored a new class of co-catalysts FeB, CoB and NiB for oxygen evolution from water oxidation and investigated PEC water splitting performance of Ta3Ns nanorod array photoanodes modified "with these metal borides.CoB and FeB were deposited on Ta3N5 nanorod arrays by a successive ionic layer adsorption and reaction (SILAR) method. The resultant photoanodes were denoted as Ta3N5-CoB and Ta3N5-FeB. The photocurrent densities of Ta3N5-CoB and Ta3N5-FeB reach 2.71 mA/cm2and 2.16 mA/cm2 at 1.23 V (vs. RHE), which are 12.3 and 9.8 times higher than that of the bare Ta3N5 photoanode, respectively. Futhermore, compared to the bare Ta3N5 photoanode, the photocurrent onset potential of Ta3N5-CoB and Ta3N5-FeB cathodically shifted by ca.300 mV and 150 mV.Synergistic effects of dual co-catalysts of metal borides were explored. High-efficiency co-catalyst NiB for oxygen evolution was further deposited on Ta3Ns-CoB and Ta3N5-FeB photoanodes by the SILAR methode. The resultant photoanodes were denoted as Ta3N5-CoB/NiB and Ta3Ns-FeB/NiB. A photocurrent density of 3.5 mA/cm2 was achieved for5Ta3N5-CoB/NiB photoanode at 1.23 V (vs. RHE), which is 15.9 times as large as that of the bare Ta3N5 nanorod array photoanode and 1.3 times as large as that of Ta3N5-CoB photoanode. Furthermore, its photocurrent onset potential is cathodically shifted by ca.400 mV in comparison with that of the bare Ta3N5 nanorod array photoanode and ca.100 mV in comparison to that of the Ta3N5-CoB photoanode. Similarly, a 4.4 mA/cm2 photocurrent density was achieved for Ta3N5-FeB/NiB photoanode at 1.23 V (vs. RHE), which is 20 times as large as that of the bare Ta3N5 nanorod array photoanode and 2 times as large as that of the Ta3N5-CoB photoanode. Its photocurrent onset potential is cathodically shifted by ca. 350 mV in comparison to that of the bare Ta3N5 nanorod array photoanode and ca.200 mV in comparison to that of the Ta3N5-FeB photoanode.