Symposium A. Green Energy Materials

Symposium A1: Energy Storage

Prof. Ulrich Stimming

Technical University of Munich/ Litricity GmbH, Germany

Date & Time: November 19 (Sun.) 13:30-14:05
Venue: Delta Building B1 B03

Topic: Energy Storage Using Polyoxometallates.

Coming soon.

Energy storage is a crucial element in transforming a fossil fuel based electricity generation to one that is essentially carbon free. Energy storage allows to decouple on a time scale the generation and consumption of electricity. It also helps to minimise the generation of waste heat which is either connected to the insufficient implementation of renewables or to nuclear power, fission or fusion alike. Today’s batteries are fairly advanced, e.g. being successfully used in electric vehicles, but using them on a grand scale requires long life times with cycle numbers well above 20,000. Currently only redox flow batteries can achieve this, like the vanadium redox flow battery (VRFB); but this technology has various serious drawbacks, such as poisonous and highly corrosive electrolyte, low energy and low power density, high costs etc. All these issues can be rectified by using polyoxometallates (POMs) as redox species in the electrolyte.

POMs are a vast class of complex ions which consist of metal-oxygen clusters where the metal content can even exceed 1000 atoms. This generates multiple redox centres in the molecule leading to a potentially high energy density. Due to its specific structure and the essence of Marcus theory the rate of electron exchange is very fast since the electron exchange is adiabatic and reorientation of the molecule and its surrounding is small, i.e. it creates only a low barrier. This allows for a high power density of the battery, a potentially very important behaviour for the battery use for grid stabilisation1. POMs are usually very stable under acidic or neutral conditions and have mostly a high solubility in water. As an example, Fig.1 shows cyclic voltammetry of SiW12 and PV14, two POMs that have been extensively tested indicating the large amount of charge available1,2. Testing in a large RFB cell shows a stable behaviour with high efficiencies (Fig.2)2.

In future work, POMs based on earth-abundant elements will considerably reduce system costs.

Fig. 1. Cyclic voltammograms (CVs) and structure of the used POMs.

(a) CVs of 1 mM SiW12 and 1 mM PV14 at a scan rate of 100 mV s–1.

(b) Polyhedral representation of SiW12.

(c) Polyhedral representation of PV142

Fig. 2. Long-term behaviour of a 1400cm2 cell: Coulombic and energy efficiency2.

Keywords: Polyoxometallates, high energy density, high power density, energy storage, redox flow battery


  1. J.Friedl, F.Pfanschilling, M.V. Holland-Cunz, R.Fleck, B.Schricker, H.Wolfschmidt, U.Stimming, Clean Energy,2019,278
  2. J.Friedl, M.V.Holland-Cunz, F.Cording, F.Pfanschilling, C.Wills, W.McFarlane, B.Schricker, R.Fleck, Energy Environ. Sci.,2018,11,3010

Symposium A2: Energy Conversion and Generation

Prof. Takao Mori

National Institute for Materials Science (NIMS), Japan

Date & Time: November 18 (Sat.) 16:15-16:50
Venue: Delta Building B1 B03

Topic: Recent developments in enhancement principles for thermoelectrics

Coming soon.

Development of thermoelectric (TE) materials is important, for energy saving via waste heat power generation [1], and IoT power sources [2]. For high TE performance, we must find ways to overcome the traditional tradeoffs between the properties, namely, between Seebeck coefficient S and electrical conductivity s, and between the electrical and thermal conductivity k [3].

For the latter aspect, in addition to various nanostructurings, intrinsic low k mechanisms have been demonstrated. Materials informatics approach [4], doping leading to lattice softening [5], heterogeneous bonding from mixed anions [6], etc.

For overcoming the first tradeoff, we have found that magnetism can be utilized to enhance the Seebeck coefficient and overall power factor (PF). Coupling of the electrical carriers with magnetic moments, can increase S, with recent advancement in magnon drag showing it can actually lead to high performance, i.e. high PF for CuFeS2 chalcopyrite [7]. It was also proposed as the origin [8] of the huge PF in metastable Fe2VAl-based thin films [9].

We have also discovered TE enhancement in paramagnetic systems, namely we show that in cases with strong coupling, this interaction “drags” the carriers, leading to an increase in the effective mass which enhances the Seebeck coefficient. This will be detrimental to the mobility but overall, enhancements to the power factor have been able to be realised in high performance TE systems, the first example demonstrated being CuGaTe2 [10]. Later this interaction was named as paramagnon drag. Magnetic ion doping enhancement has also been demonstrated for Bi2Te3 [11], for example.

Spin fluctuation was found to enhance the Seebeck coefficient in the Heusler alloy Fe2VAl [12]. Spin entropy is also known to enhance S [13].

I will discuss all these magnetic TE enhancement phenomena.

In a final topic, an interesting dual effect of small amounts of Cu doping in Mg3Sb2 was revealed. Interstitial Cu doping lowered the phonon group velocity, while doping into the grain boundaries promoted grain growth and optimum interfaces leading to very high mobilities similar to single crystals, while being a polycrystalline material with low thermal conductivity. An initial realistic 8 pair module exhibited an efficiency of 7.3%@320oC, with estimated efficiency from the actual materials being ~11%! [14]. Tuning toward room temperature yielded an initial realistic 8 pair module with an efficiency of 2.8% with temperature difference of 95 K from RT and cooling of 56.5 K [15]. Recently, a modified single element device of Mg3Sb2 was able to achieve a TE efficiency ~12% [16].


[1] L. E. Bell, Science 321, 1457 (2008), JOM, 68, 2673-2679 (2016). [2] Sci. Tech. Adv. Mater. 19, 836 (2018), MRS Bulletin, 43, 176 (2018).

[3] T. Mori, Small 13, 1702013 (2017), Energies, 15, 7307 (2022).

[4] Energy Environ. Sci., 14, 3579 (2021).

[5] Adv. Energy Mater., 11, 2101122 (2021).

[6] J. Mater. Chem. A, 9, 22660 (2021), J. Mater. Chem. A, 11, 10213 (2023) Hot article.

[7] Angew. Chem. Int. Ed. 54, 12909 (2015).

[8] Phys. Rev. B, 104, 214421 (2021).

[9] Nature 576 (7785) 85-90 (2019).

[10] J. Mater. Chem. A, 5, 7545 (2017).

[11] Mater. Today Phys., 9, 100090 (2019).

[12] Science Advances, 5, eaat5935 (2019).

[13] Sci. Tech. Adv. Mater., 22, 583-596 (2021).

[14] Joule, 5, 1196-1208 (2021).

[15] Nature Commun., 13, 1120 (2022).

[16] Advanced Energy Materials (2023)

Selected as Front Cover Article.

Keywords: thermoelectric materials, enhancement principles, devices

Symposium A3: Hydrogen Energy

Prof. Hong Yang

University of Illinois at Urbana-Champaign, USA

Date & Time: November 17 (Fri.) 13:30-14:05
Venue: Delta Building B1 B03

Topic: Understanding the Design Rules of Electrocatalyst for Oxygen Evolution Reaction

Coming soon.

Electrocatalysis often plays an essential role in the development of green energy conversion and storage technology, such as water splitting for hydrogen production. Oftentimes the slow reactions occurring at oxygen electrode that limit the system performance. In this presentation, I will present the study of structure-oxygen reduction property relationship of complex oxide electrocatalysts that have the generic form of AxByOz, where A and B can be a single metal cation or mixed cations, respectively. Some of the best-known classes include perovskite, pyrochlore, spinel, and Ruddlesden-Popper (RP) and their site-mixed solids, including high entropy oxides.  Defect engineering in these solids is particularly important for improving the activity and stability of the electrocatalysts for the oxygen revolution reaction (OER). In addition, design of interfacial structures should also help in further improving the performance at the device level. I will discuss our latest results on understanding how to regulate the cation sites and oxygen defect chemistry for enhancing the bond-stability and interface structure of key constituents and how such changes affect the electrocatalytic performance.

Keywords: Oxygen evolution reaction, Complex oxide, Electrocatalyst, Cation site, Oxygen defect chemistry

Prof. Sammy Lap Ip Chan

National Central University, Taiwan

Date & Time: November 17 (Fri.) 15:40-16:15
Venue: Delta Building B1 B03

Topic: High-Performance Hydrogen Storage Alloys for Microgrids and Remote Area Power Supply Systems

Coming soon.

In response to the drastic changes in the global climate and the impact of greenhouse effect, the general trend is to reduce our reliance on fossil fuel, and to increase substantially the contribution of renewable energy toward the energy usage. However, renewables such as solar and wind power are inherently intermittent and seasonal. Presently the trend in developed countries is to take remote communities away from electricity grid and replace it with disconnected microgrids. Microgrids can also be connected to the main grid to enhance the electricity supply stability, to provide high efficiency, and to reduce transmission and distribution losses. Microgrids can find many applications especially for the outlying islands or regional, and remote communities. Solar-hydrogen system is a relatively new concept of energy storage in microgrid and remote area power supply. Here the solar-hydrogen system uses surplus energy generated by the photovoltaic panels to produce hydrogen via a proton exchange membrane electrolyzer. The hydrogen is stored in hydrogen storage materials housed in a hydrogen tank. When there is insufficient solar power to supply the load, a fuel cell in the system will cover the deficiency by drawing hydrogen from the storage. In this presentation, we will cover several important hydrogen storage alloy systems, their characteristics, advantages and limitations in meeting the specific energy storage requirements of the solar-hydrogen system in microgrids or independent remote area power applications. We propose the application of AB3 La-Mg-Ni hydrogen storage alloy as the starting material to blend with other alloy systems, so as to develop new high-performance, cost-effective hydrogen storage composite alloys for use in the solar hydrogen system. Compared with other alloy systems, AB3 La-Mg-Ni hydrogen storage alloy is more suitable for such an application, with a large amount of hydrogen stored, low working temperature and pressure. We will use the hydrogen storage AB3/AB5 composite alloy systems as examples, which exhibit high hydrogen storage capacity and rapid adsorption/desorption rates at room temperature. Several examples of the applications of the solar-hydrogen systems are given in the presentation. We would also like to take this opportunity to introduce briefly the Australian hydrogen policy and strategic actions.

Keywords: Hydrogen Storage, Remote Power Supply, Small Grid

Symposium A4: Photocatalysis and Photosynthesis

Prof. Tzu-Chien Wei

National Tsing Hua University, Taiwan

Date & Time: November 19 (Sun.) 15:40-16:15
Venue: Delta Building B1 B03

Topic: Perovskite Solar Cell: Is it the Holy Grail of Next Generation Photovoltaic or Just Another Paper Monster?

Coming soon.

Global warming has become a serious worldwide problem because of the continuously increasing carbon dioxide emission. As a result, the 2015 Paris agreement has announced the NET zero carbon policy to be achieved in 2050. This is a big challenge for most developed countries including Taiwan. Sun is the most important and inexhaustible clean energy source in the earth. Effective utilization of solar energy could be the fastest pathway for human being to get rid of fossil fuels and their environmental concerns.

Perovskite (CaTiO3) is a kind of minerals discovered by Gustav Rose in 1839 and is named after Russian mineralogist Lev Perovski. Therefore, the chemical structures with the formula ABX3 are named perovskites. Instead of traditional oxide perovskites, halide perovskites are found to have superior optoelectronic properties such as high absorption coefficient, high carrier mobility, high photoluminescence quantum yield (PLQY), flexible spectral tunability, great defect tolerance, and so forth. Due to these advantages, halide perovskites are suitable to serve as active layers for photovoltaic applications. All-solid-state organic-inorganic hybrid perovskite solar cells (PSC) have emerged in 2012 and rapidly progressed so that the device performance of PSC attained the efficiency of power conversion (PCE) 25.8 % in 2021 (Nature 2021, 598, 444). While PSCs have become highly efficient in a decade, it is generally acknowledged three challenges, namely stability, conversion efficiency at large scale and manufacturability remain before they can become a real and competitive commercial technology. Early PSCs degraded rapidly, losing photovoltaic performance within minutes. But through compositional engineering (Nature 2015, 517, 476), bulk or interfacial passivation (Nature Photonics 2019, 13, 460), and encapsulation of devices (Energy Environ. Sci. 2022, 15, 13), nowadays PSC devices have demonstrated lifetimes of several years (Nat. Commun. 2017, 8, 15684).

The major challenge of PSC technology toward commercialization is maintaining high and robust efficiency at large scale. High efficiency lab. devices are usually made on an active area of far less than 1 cm2. However, the materials, fabrication technologies or even device structures reported in those high-efficiency devices have not necessarily been stable or even not possible to fabricate at a large scale. Consequently, maintaining high efficiencies while achieving stability in large-area modules will be a core course for the practical use of PSC. In this talk, we will share our efforts in above-mentioned PSC challenges for the past decade and perspective on PSC commercialization.

Keywords: perovskite solar cell, stability, scalability, efficiency, net zero carbon

Prof. Hin-Lap Yip

City University of Hong Kong, China

Date & Time: November 17 (Fri.) 16:15-16:50
Venue: Delta Building B1 B03

Topic: Molecularly Engineered Interfaces in Perovskite Optoelectronic Materials and Devices.

Coming soon.

In recent years, organic-inorganic hybrid perovskites have ascended as a novel category of solution-processable semiconductors, exhibiting immense potential for a plethora of optoelectronic applications, including but not limited to solar cells and LEDs. Their unique electronic, electrical, and optical properties can be finely manipulated by adjusting their compositions and crystalline structures. In this talk, our focus will rest on the design and implementation of molecularly functionalized materials aimed at modifying the interfaces within the perovskite crystal and serving as interlayers in perovskite-based devices (Fig. 1).

Initially, I will discuss how to control the dimensionality and nanostructure of perovskites through the introduction of small molecules, equipped with tailored functional groups. These groups are designed to interact robustly with perovskite crystals. By leveraging this strategy, we have successfully engineered highly stable quasi-2D perovskite solar cells [1] that exhibit significant enhancements in stability and efficiency. Additionally, we have constructed highly efficient blue [2] and white [3] emitting perovskite LEDs. Subsequently, we will delve into the application of our knowledge learned from interface engineering in organic solar cells to design novel electron and hole transport conjugated materials possessing optimal interfacial properties for perovskite solar cells. These properties will enhance surface defect passivation functionality and improve the charge collection efficiency of perovskite solar cells [4-5], as well as organic/perovskite tandem solar cells [6-7].


(1) Q. Yao, H.-L. Yip, et al, Adv. Mater. 2020, 32, 2000571

(2) Z. Li, H.-L. Yip, et al, Nat. Commun. 2019, 10, 1027

(3) Z. Chen, H.-L.Yip, et al, Joule, 2021, 5, 456

(4) J. Wang, Z. Zhu, H.-L. Yip, A. K.-Y. Jen, Nat. Commun. 2020, 11, 177

(5) T. Niu, Q. Xue, Y. Li, H.-L. Yip, et al, Joule., 2021, 5, 249

(6) S.-Q. Sun, H.-L. Yip, Y. Xie et al, Adv. Energy. Mater., 2023, 13, 2204347

(7) Y. An, H.-L. Yip et al, Adv. Mater. 2023, 35, 2306568

Keywords: Perovskite solar cells; Tandem cells; Perovskite LEDs, Molecular Interfaces; Passivation

Fig. 1. Schematic of molecular interfaces in perovskite devices and semiconductors.