ENHANCED PERFORMANCE OF NICKEL-IRON LAYERED DOUBLE HYDROXIDE AS AN OXYGEN EVOLUTION REACTION CATALYST THROUGH INTERCALATION
Open Access
- Author:
- Dong, Yan
- Graduate Program:
- Materials Science and Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- September 30, 2019
- Committee Members:
- Sridhar Komarneni, Dissertation Advisor/Co-Advisor
Sridhar Komarneni, Committee Chair/Co-Chair
Donghai Wang, Committee Member
Hojong Kim, Committee Member
Ramakrishnan Rajagopalan, Outside Member
John C Mauro, Program Head/Chair - Keywords:
- layered double hydroxde
pH-near-neutral condition
intercalation
in-situ anion exchange
oxygen evolution reaction - Abstract:
- Water splitting is a promising way to produce hydrogen using electricity generated from sustainable but intermittent energy sources such as the sun and wind. The anodic oxygen evolution reaction (OER) is the bottleneck for water splitting due to its sluggish kinetics. In order to lower the cost, highly-active, robust and cost-effective OER catalysts need to be developed and used to overcome the reaction barrier of OER, especially in neutral or near-neutral pH conditions. Compared to alkaline or acidic conditions, pH-neutral or pH-near-neutral conditions are expected to be less corrosive and safer. In addition, natural water sources such as seawater could be used directly under such conditions, which could further lower the cost. However, OER catalysts for pH-neutral or pH-near-neutral conditions are underdeveloped and efforts are needed to develop efficient OER catalysts based on earth-abundant elements to replace the precious RuO2 and IrO2 catalysts. Here, we discover for the first time that the anion-exchange properties of nickel-iron layered double hydroxides (NiFe LDH) intercalated with large organic anions can be exploited to make them excellent OER catalysts for pH-near-neutral borate electrolyte (K-Bi, pH=9.2). In this thesis, NiFe LDHs intercalated with different dicarboxylate anions were synthesized and were studied as OER catalysts in the K-Bi electrolyte (pH=9.2). Sebacate anion intercalated NiFe LDH (NiFe LDH Seb) and suberate anion intercalated NiFe LDH (NiFe LDH Sub) were found to be excellent OER catalysts which outperformed RuO2 in the K-Bi electrolyte (pH=9.2). Both of them could deliver a 1 mA/cm2 current density and a 2 mA/cm2 current density with relatively lower overpotentials compared to RuO2. Moreover, these materials also showed great stability for at least 24 hours. Besides, all the NiFe LDHs intercalated with dicarboxylate anions showed good OER performances in K-Bi (pH=9.2) electrolyte. It is discovered that the good OER performance of the dicarboxylate anions intercalated NiFe LDHs can be attributed to the “structural instability” induced in-situ anion exchange process during the OER in which borate anions can enter the interlayers of LDH and facilitate the activation of more Ni sites. This study shows that the “structural instability” caused by pillaring of transition metal LDHs with large organic anions could be a promising way to make highly-efficient OER catalysts for pH-neutral or pH-near-neutral electrolytes. Moreover, the effects of interlayer spacing and intercalate on the OER performances of NiFe LDHs are elucidated, which may shed some light on the future development of layer-structured electrocatalysts.