Boosting Oxygen Evolution Reaction Using Defect Rich Ultra-Thin Ruthenium Oxide Nanosheets in Acidic Media
Authors: Zeng Lin , Zhao Zhiliang , Zhang Jianshuo , Li Xiaomin 
Published: December 2020

Hydrogen is regarded as the most promising energy carrier. The pure hydrogen produced from electrochemical water splitting by using renewable energy is the most attractive and effective approach.[1] In comparison to alkaline water electrolysis, proton exchange membrane water electrolyzers (PEMWEs) could operate at higher current densities, lower ohmic loss, more compact system design, faster system response and more stable towards load-cycling and shutdowns. [2] The sluggish kinetics of oxygen evolution reaction (OER) at the anode of PEMWEs has restricted its practical applications. To date, iridium (Ir) metal and its oxide are usually selected as the state-of-the-art catalyst for OER due to their robust and long-term durability under the harsh acidic conditions. Nevertheless, Ir is an extremely scarce element, and its price has been doubled in the past few years. The development of low cost and highly effective electrocatalyst for OER in an acidic medium is urgently needed but remains a great challenge.
In this work, we have prepared an ultra-thin RuO2 nanosheets by a simple molten salt method. High resolution STEM results show that the as-prepared RuO2 nanosheets is about 1-2 nm in thickness and hold a large number of defects, like Ru vacancy, grain boundary and amorphous. Toward OER, the as-prepared RuO2 nanosheets demonstrate an outstanding OER activity in acidic electrolyte, with an overpotential of only 199 mV for reach the current density of 10 mA cm-2
geo at a catalyst loading of 125 μg cm-2
geo. At the overpotential of 230 mV, the specific and mass activities of RuO2 nanosheets electrode is up to 0.89 mA cm-2
oxide and 0.516 A mg-1
Ru, which is 14.9 and 80.5 times higher than that of commercial RuO2
catalyst, respectively. Density functional theory (DFT) calculations (Figure 2e and 2f) indicated that the Ru vacancy defect on RuO2 surface could servers as the highly active site for remarkably weaken the binding energies of *O as compared to that of *OOH, which decrease the energy gap between ΔGO and ΔGOOH and thus dramatic enhanced OER performance. We also applied the catalysts in a homemade PEMWE device, at the applied cell voltage of 1.65 V, the current density of the RuO2 nanosheets catalyst cell reaches 0.93 A cm-2, which is almost 3 times larger than that of the cell with commercial RuO2 catalyst (0.31 A cm-2) at the same conditions, demonstrating that the RuO2 nanosheets possess great potential toward developing high performance PEMWEs.
This work is under progress. Meanwhile, further characterizations, including XRD, XPS and more detailed morphology and electrochemical performance characterization of the RuO2 nanosheets catalyst will be presented at the meeting.
The work described in this paper was financially supported by the Shenzhen Clean Energy Research Institute (No. CERI-KY-2019-003), Shenzhen Peacock Plan (KQTD2016022620054656), Shenzhen Key Laboratory project (ZDSYS201603311013489), The authors acknowledge the assistance of SUSTech Core Research Facilities.
References
1. Shi, Q.; Zhu, C.; Du, D.; Lin, Y., Robust noble metal-based electrocatalysts for oxygen evolution reaction. Chem Soc Rev 2019, 48 (12), 3181-3192.
2. Kibsgaard, J.; Chorkendorff, I., Considerations for the scaling-up of water splitting catalysts. Nature Energy 2019, 4 (6), 430-433.

Figure 1