Abstract
The high electrochemical stability of Zirconia (ZrO2) at high potentials strongly suggested it as an alternative to carbon supports, which experience reduced efficiency due to some corrosion problems particularly during prolonged electrocatalysis activity. However, the use of ZrO(2)was limited by its low electrical conductivity and surface area. In this work, we developed a methodology for synthesizing monoclinic ZrO(2)NPs with increased surface area and improved electrical/electrocatalytic characteristics without using any carbon-based co-support material or any metallic nanoparticles. In this context, for the first time, highly defective hydroxyl-functionalized ZrO(2)NPs (designated here as ZT NPs) were prepared by a hydrothermal route in the presence of sodium tartrate as a mineralizer. XRD analysis demonstrated that the produced zirconia was semicrystalline microspheres, consisting of monoclinic ZrO(2)NPs with high lattice defects. The addition of tartrate ions decreased the crystallite size and increased the defects and microstrain. At the same time, the alkaline hydrogen evolution reaction (HER) catalytic activity of ZrO(2)NPs was significantly increased when using sodium tartrate as mineralizer; the overpotential required to obtain 10 mA cm(-2)(eta(10)) dropped down from 490 to merely 235 mV, while an exchange current density (j(o)) increased 12 times to 0.22 mA cm(-2). The presence of structural defects (revealed by XRD) and the increased number of active surface sites contending O-H groups (evidenced from ATR-FTIR and XPS) as well as the enhanced electrochemical active surface area (confirmed from double-layer capacitance measurements) were the main reasons behind the high catalytic performance. The ZrO(2)NPs catalytic activity increased even further during the long-term stability tests under severe cathodic conditions (ZT*, ZrO(2)NPs obtained after the long-term stability, hasj(o)= 0.47 mA cm(-2)and eta(10)= 140 mV), approaching the activity of Pt/C catalyst. This process was assisted by mineralizer removal from the catalyst (testified by XPS). Our studies revealed that ZT* are characterized by larger electroactive surface area and more structure defects compared to ZT, where surface area and microstrains resulting from surface hydroxylation open cavities in zirconia structure.