Research background
Motivation statements
Energy storage and conversion devices
For metal-air batteries, the specific energy values are given, both including and excluding the oxygen mass. Because these metal-air batteries use an anode made of pure metal and a reactant of oxygen from the ambient air, the systems provide higher specific energy values than conventional batteries.
Electrocatalysts
Metal-air batteries
Oxygen electrochemistry
Thus, finding efficient oxygen reduction electrocatalysts along a low-cost and efficient four-electron pathway faces current challenges. Thus, the discovery of efficient bifunctional electrocatalysts and the demonstration of reaction mechanisms for the application of metal–air batteries and fuel cells face current challenges.
Mechanism of metal-air batteries
The cell configuration of organic/aprotic Li and Na-air batteries is as follows: Li or Na metals | Organic electrolytes | Separator | Organic electrolytes | Cathodes. The cell configuration of hybrid Li and Na-air batteries is as follows: Li or Na metals | Organic electrolytes | Ion-conducting solid membrane | Aqueous electrolytes | Cathodes.
Alkaline water electrolysis
Background and mechanism
Electrocatalysts
Efficiency calculation
CO 2 conversion technology
- Background
- Electrochemical conversion
- Electrocatalysts
- Next generation CO 2 conversion devices
As briefly introduced in Chapter 1.4.2, the electrocatalysts for CO2 conversion using electrical energy require selective electrochemical activity for the CO2 reduction reaction, and not HER. If this chemistry is applied for the purpose of CO2 conversion, the cathodic reaction using the acidity of CO2 can be defined as equation 1.30 derived from equations 1.27-1.29.
Design principles for oxygen reduction activities on perovskite oxide catalysts for fuel cells and metal-air batteries. Fe/N co-doped carbon materials with controllable structure as highly efficient electrocatalysts for oxygen reduction reaction in Al-Air batteries.
Experimental techniques
- Sol-gel process
- Electrospinning method
- High-energy ball-milling process
- Half-cell measurements
- Reference electrodes
- Reversible hydrogen electrode calibration
- Catalyst ink and electrode preparation for RDE/RRDE test
- Electrochemical testing on RDE/RRDE
- iR compensation
- ECSA technique
- Full-cell measurements
- Electrode preparation
- Hybrid Li-air cells
- Seawater batteries
- Water electrolysis
- Hybrid Na-CO 2 cells
- Aqueous Zn- or Al-CO 2 cells
The gas diffusion layer coated with the catalyst was placed in the chamber of the test set and. A titanium wire was used as the current collector of the cathode, and the aqueous electrolytes were saturated with CO2 for electrochemical measurements in hybrid Na-CO2.
- Introduction
- Experimental
- Preparation of IGnP, NSC, and NSC@IGnP composite
- Preparation and assembly of a hybrid Li-air battery
- Results and Discussion
- Material characterizations
- Half-cell configured electrochemical analysis
- Full-cell measurements by hybrid Li-air batteries
- Conclusion
- References
Interestingly, the morphology of the composite was characterized by an IGnP-like cloud surrounding the NSC nanorods. X-ray diffraction (XRD) patterns are analyzed with Rietveld precision to identify the crystal structure of the NSC nanorod (Figure 3.2d).
- Introduction
- Experimental
- Preparation of air electrodes
- Characterization and electrochemical measurements on a half cell
- Preparation and assembly of seawater batteries
- Results and Discussion
- A synthetic procedure and structural characterizations
- Half-cell configured electrochemical analysis
- Full-cell measurements by seawater batteries
- Conclusion
- References
PPy/C and carbon felt were used as comparative materials to distinguish bf- PPy+Co3O4@CF peaks. Cathodic currents, however, bf-PPy+Co3O4@CF shows better performance than that of bi-Pt/C+IrO2 me. The anodic CV scan of bf-PPy+Co3O4@CF measured under seawater is shown in Figure 4.7d.
Cycling performance of seawater battery using bi-Pt/C+IrO2 and bf-PPy+Co3O4@CF at current density of 20 mA g-1.
Introduction
ABO3 perovskite oxides (A: rare earth or alkaline earth metal element, B: transition metal ion) have received considerable attention as potential alternatives to noble metal-based catalysts (e.g. RuO2 . and IrO2 ) due to their strong catalytic activity, robust stability , and compositional flexibility.8, 9 Much effort has therefore been devoted to understanding the mechanisms of OER and HER on perovskite oxides, and molecular orbital studies have suggested that cobalt-based oxides can be used as active catalysts in OER and HER. 10 Among the various ABO3 perovskite oxide catalysts, La1 -. Both theoretical and experimental investigations on transition metal dichalcogenides (TMDs) revealed the great potential of TMDs as hydrogen generation catalysts due to their high catalytic activity; robustness against CO, CO2 and O2; affordability; and scalability.14,15 Among the various TMDs, molybdenum diselenide (MoSe2) is considered a promising HER catalyst due to its relatively superior electrochemical catalytic activity and chemical stability compared to other TMDs.16,17 The Gibbs free energy of MoSe2 for hydrogen adsorption is close to zero, and its hydrogen coverage is larger than that of other TMDs.17 Due to low conductivity of the intrinsic 2H phase MoSe2, MoSe2-based composite structures, such as MoSe2/carbon cloth,16 MoSe2/n+ however p-Si,18 and MoSe2/graphene,19 have typically been used to enhance the electrochemical activity of intrinsic MoSe2. In addition, inducing the semiconducting (2H) to metal (1T) phase transition in TMDs has been considered to improve the performance of TMDs-based composite electrochemical catalysts because the metal phase can enhance their intrinsic electrocatalytic nature.20 However, the phase transition process is of TMDs is rather complex and time-consuming, and it requires an inert environment due to the highly reactive materials involved, such as alkali metals.20,21.
This charge transfer is expected to increase the intrinsic conductivity of MoSe2 and increase the amount of Co-O and Co-OH in the LSC, which can enhance the water splitting catalytic activity.
Experimental
- Synthesis of MoSe 2
- Synthesis of LSC
- Synthesis of Catalysts
- Material characterizations
- Half-cell analysis
- Overall water splitting test
- Calculation details
- Model systems for calculation
- Surface energy calculations
To find the optimum ratio for the LSC&MoSe2 catalyst, LSC and MoSe2 were high-energy milled with 10 wt% Ketjen black EC-600JD (KB) using a planetary ball mill system (PM-200, Retsch, Germany). The BET surface area and pore size of LSC&MoSe2 and LSC were investigated using N2 desorption/adsorption physisorption analyzer (ASAP 2420, Micromeritics Instruments). The LSC&MoSe2 and LSC used in the TGA analysis were exposed to wet air for 24 h to absorb moisture.
To construct the LSC MoSe2 heterostructure, each plate model for the LSC and MoSe2 surface.
Results and Discussion
- Morphological and structural properties of LSC&MoSe 2
- Electrochemical performance
- Analysis of LSC&MoSe 2 properties
- Synergetic effect for improved electrochemical performance
- Theoretical elucidation of charge transfer in LSC&MoSe 2
- Overall water splitting of LSC&MoSe 2 || LSC&MoSe 2
- Energy efficiency calculation
The pore size of LSC&MoSe2 was investigated using the Barrett–Joyner–Halenda (BJH) method. Co 2p XPS spectra of LSC&MoSe2 and LSC consisting of two spin-orbit doublets and two satellites. The improved catalytic performance of LSC&MoSe2 was investigated by means of electrochemical impedance spectroscopy (EIS) analysis.
The chemical state of LSC&MoSe2 after the stability test was further investigated by XPS analysis.
Conclusion
We calculated the energy efficiency of the total water electrolysis at the current density of 100 mA cm-2 as follows. Since the electrolysis cell operates close to 2.3 V at 100 mA cm-2, the energy required to produce 1 kg of H2 can be calculated as follows. Since the electrolysis cell operates at 0.23 W cm-2, the energy required to produce 1 kg of H2 is calculated to be 61.65 kWh.
The energy efficiency can be calculated by dividing the theoretical specific energy for 1 kg H2 production, i.e. 39.4 kWh.
Furthermore, the charge-discharge profiles at various current densities under CO2-saturated NaOH solution and seawater are investigated as shown in Figure 6.11c. Also, the H2 generation and CO2 conversion rates were similarly observed under CO2-saturated seawater (Figure 7.12e). As shown in Figure 7.27a and Equation 7.9, the oxidation reaction under CO2-saturated 1 M KOH is revealed as oxygen evolution reaction (OER).
We investigated the anodic RDE polarization profile (Figure 7.27c) in CO2-saturated seawater using a Pt/C+IrO2 catalyst as follows.
Supplementary References for Table 5.1, 5.2, and 5.9
Efficient CO₂ utilization via a hybrid Na-CO₂ system based on CO₂ dissolution
- Introduction
- Experimental
- Half-cell configured electrochemical analysis
- Characterization techniques
- Full-cell measurements
- Results and Discussion
- The proposed hybrid Na-CO 2 cell and its reaction mechanism
- Half-cell configured electrochemical analysis
- Performance and stability of hybrid Na-CO 2 cell
- Reversibility of hybrid Na-CO 2 cell
- Conclusion
- References
The cathodic electrochemical profiles were carefully examined using a cyclic voltammetry (CV) technique on the Pt electrode (Figure 6.3a). For depth analysis, the kinetics of these electrochemical reactions were interpreted by Tafel slope analysis (Figure 6.3b). The complete discharge profile was investigated in a CO2-saturated NaOH solution (Figure 6.4b) with a mechanical supplement by replacing the Na metal anode.
It is noteworthy that the continuous enrichment of NaHCO3(aq) in the aqueous media from the discharge does not affect the discharge performance as shown in the 1,000 hour discharge profile (Figure 6.4b).
Highly efficient CO 2 utilization via aqueous zinc- or aluminum-CO 2 systems for hydrogen
Introduction
The dissolution of CO2 in an aqueous electrolyte is thermodynamically spontaneous and forms carbonic acid. By employing kinetically efficient hydrogen evolution reaction (HER) using the acidity of CO2 as a cathodic reaction, this new system could simultaneously generate electricity and H2 powered by the electrochemical oxidation of Zn or Al metals. In addition, inoperando gas chromatograph measurements have shown that our aqueous cell could perform comparable discharge rate to conventional Zn/Al-air cells with continuous utilization of CO2.
These Zn/Al-CO2 systems thus have the potential for efficient CO2 removal, power and hydrogen production in an era of pursuing a clean energy source.
Experimental
- Catalysts preparation and characterization techniques
- Half-cell analysis
- Full-cell measurements
Half-cell measurements were performed in a three-electrode configuration, using a platinum wire as the working electrode and counter electrode with an Ag/AgCl reference electrode (filled with saturated KCl) in 1 M potassium hydroxide (KOH, Sigma-Aldrich Co.) aqueous solution and seawater (taken from the Ulsan Sea and filtered to remove visible impurities). Each catalyst was prepared into a catalyst ink by dispersing 10 mg of the catalyst in 1 ml of a binder solution of ethanol: isopropyl alcohol: 5 wt. % Nafion solution (Sigma-Aldrich Co., volumetric ratio), followed by a bath sonication procedure. For the alkaline electrolyte, 6 M KOH and 4 M aqueous NaOH solution were used for the Zn and Al systems, respectively.
The cathode was prepared by electrically spraying the catalyst ink onto a gas diffusion layer (Toray carbon paper TGP-H-090, Fuel Cell Store Co.) with a loading density of 2 mg cm-2.
Results and Discussion
- The proposed Zn- or Al-CO 2 systems and their electrochemical mechanism
- Half-cell configured electrochemical analysis
- Structural and Physical Characterization for Catalysts
- Full-cell performance and comparison to other works
- Continuity of H 2 generation and CO 2 conversion
- Reversibility of the aqueous Zn- or Al-CO 2 systems
Discharge profiles measured at high current densities (10 and 50 mA cm-2) over 50 h for Zn/Al-CO2 systems using Pt/C are shown in Figure 7.14. As shown in Figure 7.27c and Equation 7.10 above, from the similar oxidation potential region of OER, the oxidation reaction under CO2-saturated seawater can follow CER. As expected from the anodic RDE profiles (Figure 7.27), both Zn- and Al-CO2 systems are rechargeable under both CO2-saturated 1 M KOH and seawater, as shown in the I-V charging profiles (Figure 7.28a and Figure 7.28c).
The charge plateaus were obtained near 2.5 and 3.0 V for Zn and Al system, respectively, for both CO2-saturated KOH solution and seawater (Figure 7.28b and Figure 7.28d).
Conclusion
Therefore, Zn/Al-CO2 systems are reversible/rechargeable and do not regenerate already used CO2, which truly fulfills the purpose of true CCUS technology. These proposed Zn/Al-CO2 systems could potentially serve as a new technology for CO2 utilization in the era of searching for a clean energy source.
Jeongwon Kim, Ohhun Gwon, Ohhun Kwon, Javeed Mahmood, Changmin Kim, Yejin Yang, Hansol Lee, Jong Hoon Lee, Hu Young Jeong, Jong-Beom Baek* and Guntae Kim*. Changmin Kim, Ohhun Gwon, In-Yup Jeon, Youngsik Kim, Jeeyoung Shin, Young-Wan Ju*, Jong-Beom Baek* and Guntae Kim* “Skylike graphen-nanoplader på Nd0.5Sr0.5CoO3−δ nanorods som en effektiv bifunktionel elektrokatalysator til hybrid Li-air batteries”. Young-Wan Ju,† Seonyoung Yoo,† Changmin Kim, Seona Kim, In-Yup Jeon, Jeeyoung Shin, Jong-Beom Baek* and Guntae Kim* “Fe@N-Graphene Nanoplatelet-Embedded Carbon Nanofibers as Efficient Electrocatalysts for Oxygen Reduction Reactions ” (Udvalgt som forsideartikel) Adv.
Yejin Yang, Jeongwon Kim, Arim Seong, Changmin Kim, Ohhun Kwon, In-Yup Jeon, Yunfei Bu*, Jong-Beom Baek* and Guntae Kim* "A pH-Independent and Durable Ruthenium-Based Catalyst with a Functionalized Edge Site for Efficient Hydrogen Evolution' will be submitted.
