The fuel cell mode is powered by reverse reactions of the water splitting mode. Proton Exchange Membrane (or Polymer Electrolyte) Water Electrolyzer PEMFC PEMWE.
Introduction
Needs for research related to hydrogen and oxygen
In addition, water splitting from renewable energy sources such as solar cells and wind power is considered the most promising route for carbon-free, environmental and sustainable hydrogen production (Figure 1.2).5 However, it is difficult to use in efficiently since the water splitting overpotential is still high. Plot of summarized distributions of non-noble metal-based carbon electrocatalysts for HER under different pH ranges and distributions of different non-noble metal-based carbon compositions corresponding to pH conditions (acidic, alkaline and wide pH medium) .
Hydrogen and oxygen related energy conversion reactions
- Principles of hydrogen and oxygen related reactions
Useful notions in hydrogen and oxygen related test
- Equilibrium potential
- Onset potential
- Current density
- Tafel slope
- Electron transfer number (n)
- Potential gap
When η = 0, the current density from the equation is called exchange current density (i0), which represents the intrinsic activity of the catalysts under equilibrium conditions. In general, the potential gap (∆E) between an ORR current density of −3 mA cm−2 and an OER current density of 10 mA cm−2 for ORR/OER and the potential gap (∆E) between an HER current density of −10 mA cm −2 and an OER current density of 10 mA cm−2 for HER/OER are used as performance evaluation indicators.
Factors affecting electrochemical reactions
- Surface area
- Electron conductivity
- Stability
- Catalytic activity of catalysts
First, since the oxygen solubility of liquid electrolytes is relatively low, it is critical to optimize the hydrophobicity of the electrodes and the surface area of active sites. The activity is expressed by the value of overpotential to a certain value of current density from ref.
Utilizations of hydrogen and oxygen related reactions
- ORR/OER – rechargeable metal-air (or O 2 ) cells
- HOR/ORR: fuel cells (PEMFC, AEMFC)
- HER/OER: water electrolyzer (PEMWE, AEMWE)
- HER/OER & HOR/ORR: regenerative fuel cells (RFCs)
Water electrolysis can be divided into PEMWE (proton exchange membrane water electrolyzer) and AEMWE (anion exchange membrane water electrolyzer) according to the electrolyte used in the electrolysis cells. Schematic representation of an AEM-URFC as an energy storage device for vehicle and grid applications.
Scope
The AEM-URFC stores renewable energy as H2 while in electrolyzer mode and then uses that H2 to produce electricity on demand when in fuel cell mode.
Introduction
Bifunctional hydrous RuO2 nanocluster electrocatalyst embedded in carbon matrix for efficient and durable operation of rechargeable zinc-air batteries. Coating cathode and/or anode materials with carbon has been widely used as a key strategy to improve electrical conductivity throughout electrodes.33-35 Electroactive materials can be easily synthesized with carbon by reducing carbon precursors in a reductive gas environment at temperatures between higher than the thermal decomposition temperature of the precursors and lower than reduction temperature of the active materials. Two points are emphasized in our strategy to guarantee bifunctional electroactivities of RuO2 for ORR and OER simultaneously: (1) partially hydrated RuO2 as catalysts and (2) carbon coating on the catalyst particles.
We introduced electrical conductivity of the catalyst layers by embedding RuO2 or more precisely h-RuO2 nanoparticles in a carbon matrix phase (RuO2@C). The RuO2@C was synthesized by annealing micelles consisting of ruthenium oxide surrounded by double hydrophilic block copolymers of poly(ethylene oxide)-block-poly(acrylic acid) (PEO-b-PAA) as a template. During the annealing process, hydrous ruthenium oxide core was crystallized and the shell of PEO-b-PAA was converted to a continuous carbon phase surrounding partially water-rich RuO2. Both ORR and OER electroactivities were significantly enhanced by the incorporation of hydrous RuO2 into the carbon phase.
RuO2@C showed the smallest potential gap between ORR during discharge and OER during charge, confirming its improved reversibility compared to Pt/C and ah-RuO2 and Zn-air cell data reported in the literature.
Experimental Method & Materials
- RuO 2 @C Synthesis
- Characterization
- Catalyst inks
- Electrochemistry
- Zn-air battery
Pt/C (20 wt.% Pt loading on carbon black, Alfa Aesar) was also used as a catalyst composite for comparison. Hg/HgO (XR400, Radiometer Analytical) and Pt wire were used as reference and counter electrodes. All potentials in this work were reported in VRHE (V vs. RHE; RHE = reversible hydrogen electrode), even if the potential values were read from the potentiostats in VHg/HgO: VRHE = VHg/HgO.
At the same time, +0.4 VHg/HgO was applied to the ring electrode of RRDE to detect the peroxide formed by the disk electrode by completely oxidizing the peroxide. The OER polarization voltammograms at 10 mV s–1 were obtained in the N2-saturated electrolyte between +0.35 VHg/HgO and +0.9 VHg/HgO at 1600 rpm. 100 µl of catalyst ink was loaded onto a carbon-GDL electrode (geometric area = 2.834 cm2) and the catalyst-loaded electrode was dried at 80 oC for 80 °C.
Zn-air cells were galvanostatically discharged and charged at different currents by a potentiostat (Bio-Logic, VMP3).
Results and Discussion
- RuO 2 @C nanoclusters as catalyst
- ORR
- OER
- Rechargeable Zn-air battery
RuO2@C showed the well-defined X-ray diffraction (XRD) patterns of RuO2 when the annealing temperature was higher than 350 oC (Figure 2.3a-f). On the other hand, the hydrous form (h-RuO2) was favored in terms of electron transfer number (n) especially at low overpotentials (Figure 2.6b). Despite its strength at the onset potential, the hydrous h-RuO2 form showed severe weakness in stability (Figure 2.9b).
RuO2 dissolution during OER is one of the possible reasons for the OER instability, especially in h-RuO2.25, 48 A broad anodic peak was found at 1.6 VRHE for h-RuO2 in the initial anodic scan of potential ( figure 2.9a). The overpotential advantage of RuO2@C was evident in the OER stability: the potential held steady at < 1.6 VRHE at 5 mA cm-2 over 40 h (Figure 2.9d). Reversible operation of Zn-air batteries (Figure 2.14a) was realized by using the bifunctionality of RuO2@C (Figure 2.15).
Stable potential profiles were obtained in the presence of RuO2@C up to fast charging at 200 mA. The smaller ΔEOER-ORR of RuO2@C indicates the higher degree of reversibility between ORR and OER. a) The homemade Zn-air cell.
Conclusions
Performance of rechargeable zinc-air batteries of various electrocatalysts published in the literature. V) Cycle test condition Atmospheric reference RuO2 nanoclusters embedded in.
RuO 2 nanocluster as a 4-in-1 electrocatalyst for hydrogen and
Introduction
Two issues are most challenging in the field of electrocatalysts for water electrolysis: (1) bifunctional catalysts covering both HER and OER; and (2) HER or OER catalysts that work over a wide pH range.68-70. However, bifunctional HER/OER catalysts covering both reactions for water electrolysis have been reported in a limited manner. Ru-based catalysts have been considered as candidates for bifunctional HER/OER catalysts, which is supported by two recent publications.80, 81 Bifunctional catalysts probably simplify water electrolysis systems and reduce their development cost, because a single catalyst covers both electrodes.
5, 70, 84 Therefore, it is difficult to combine the best HER catalysts with the best OER catalysts at fixed pH for water electrolysis. 56, 86, 87 On the other hand, an electrolyte around pH 7 is the poorest medium for water electrolysis because both H2 and O2 are produced from water molecules instead of H+ and OH–. Aqueous electrolysis based on neutral media benefits from safety, cost and corrosion-free conditions when possible.
91 A symmetric electrolyzer based on a single catalyst was realized, characterized by low overvoltage, which is superior to the asymmetric electrolyzer based on Pt and Ir, which is considered the best pair for water splitting.
Experimental Method & Materials
- Materials
- Characterization
- Catalyst inks
- Electrochemistry
- Water splitting
- Alkaline anion exchange membrane water electrolyzer (AEMWE)
Partial hydration improved OER kinetics on RuO2: the current at 1.6 VRHE of a partially hydrated RuO2 was more than 10 times higher than that of totally anhydrous RuO2. The dried suspension was annealed at 400 oC for 2 hours to form x-RuO2@C. ah-RuO2; 30 to 50 nm primary particles from Sigma-Aldrich) and completely hydrous RuO2. h-RuO2; 100 to 200 nm primary particles from Alfa Aesar) were used as received for comparison (Figure S2). The polarization curves were obtained in 3-electrode configuration including RRDEs by a potentiostat (Bio-Logic VMP3).
The HER and OER polarization voltammograms at 10 mV s–1 were obtained in N2-purified electrolytes at 1600 rpm. Unless otherwise stated, all polarization curves were iR (f = 85 %) corrected using the EC-Lab software. Linear sweep voltammograms were obtained between 1.4 Vsel to 2.0 Vsel at 20 mV s-1 before potentiostatic operations at 1.6 Vsel.
Electrochemical impedance spectra (EIS) were obtained at 1.6 V cells in 30 kHz to 30 mHz with a sinusoidal amplitude at 10 mV.
Results and Discussion
- x-RuO 2 @C as catalyst
- HER
- OER
- Water splitting
- Tetra-functionality: ORR & HOR in addition to HER & OER
문헌에서 산성 및 중성 매질에서 0.27-RuO2@C보다 더 높은 OER 전기활성도를 나타내는 촉매를 찾는 것은 어려웠습니다(그림 3.6 및 표 3.2). 지난 7년 동안 함께 해주신 송형곤 교수님과 ECLA 회원님들께 감사드립니다. 박사. 늘 따뜻하게 다가와서 많은 조언을 해준 김영수 선생님, 저의 실험의 밑거름이 되어준 누나 명희 선생님. 약간의 말다툼 끝에 친해진 영훈. , 그리고 귀족으로 기억되는 경기. 같은 반 친구로 함께 학교에 입학했지만 그는 여러 면에서 나보다 나이가 많았다. 인생을 살아온 정석이사님, 누구보다 성숙한 지은이사님, 박사님에게 감사의 말씀을 전하고 싶습니다. 많은 이야기를 나누지 못해 아쉬웠던 델리몬, 그리고 함께했던 에클라 멤버들.
그리고 함께해준 많은 친구들, 선후배들에게도 큰 감사 인사를 전하고 싶습니다. 내 영혼의 안식처가 되어준 시민교회에 감사드립니다. 함께 사역했던 목회자들과 시민교회의 많은 식구들, 특히 김승태 목사님께 감사의 말씀을 전하고 싶습니다.
그리고 저의 무모한 선택과 도전에도 불구하고 믿음으로 옆에 있어준 가족들에게도 감사하다는 말씀 전하고 싶습니다. 떨어져 있어도 항상 함께 있다는 것을 깨닫게 해주시고 늘 따뜻하게 대해주신 일본인 어머니 이치가와에게 늘 기도로 함께해주셔서 감사합니다. 또한 글로 표현하지 못한 많은 분들께도 감사의 마음을 전하고 싶습니다.
