This proposal discuses how to innovate "electricity-material energy conversion technologies" that can generate, convert, and store electrical energy using interconversion with materials. The sophistication and diversification of this technology will solve the problems of supply-demand gap due to spatio-temporal variability and localization of suitable locations for renewable energy, and lead to the effective use of renewable energy. The massive integration of renewable energy will require the mass introduction of devices that utilize electric-material energy conversion, such as storage batteries, fuel cells, and electrolysis. In this proposal, we focus on the reaction field that governs device characteristics and suggest directions for the development of materials and devices that realize a wider operating environment as an energy infrastructure and a more ideal reaction environment in terms of energy efficiency and reaction rate. In particular, we introduce the concept of "electrical-material energy conversion reaction field". This represents the control factors that govern device characteristics, including not only the components such as reaction substrates, charge carriers (electrons and ions), electrode materials, and electrolyte materials, but also the reaction environment variables such as temperature, pH, and voltage. By establishing a cross-device science of reaction fields, it is expected to accelerate the creation of new technologies for electrochemical materials and devices, in which Japan has an advantage, and to accelerate research and development through technological integration among devices.

We propose the following activities or policies: 1. Promotion of R&D projects that contribute to the circulation of knowledge among researchers in different fields related to electricity-material energy conversion technology, 2. Development of research infrastructure to encourage new entrants from different fields, 3. Promotion of materials and device development using informatics and establishment of R&D system.

In order to realize a sustainable society, including a carbon-neutral society, renewable energies with low environmental impact must be introduced in large quantities as an alternative energy source to fossil resources. Renewable energies have the disadvantages of mismatch between supply and demand due to time variability and the localization of suitable locations. To overcome these problems, energy storage systems and the conversion of renewable energy into fuel (energy carriers) must also be introduced on a large scale. However, simple implementation of existing technologies is far from enough to realize a sustainable society. For example, electrochemical systems such as storage batteries, hydrogen fuel cells, and water electrolysis (hydrogen production) often require the use of scarce resources when operated in the reaction environments currently in use. It raises concerns about resource constraints. In other words, resource constraints are caused by the reaction environment (temperature, pH, voltage, etc.) of electrochemical systems. To address this problem, it is expected to realize a reaction environment that is milder and more resource-efficient than before. The creation of innovative material and device technologies is essential for this. In addition, from the perspective of mass adoption of renewable energy, a need has arisen for materials and devices that can absorb sudden environmental changes as infrastructure to follow the variability of renewable energy. Furthermore, electrochemical devices are expected to expand into new application fields, such as synthesis of chemical products by CO2 electrolysis and electrochemical processes for manufacturing materials such as steel and cement. In other words, electrochemical systems have an important place in the infrastructure of a carbon neutral society. In particular, there is a need to expand the reaction field to solve from resource constraints and to meet new system demands.

To address these issues, this proposal proposes to promote the creation of materials and devices that contribute to the expansion of the electric-material energy conversion reaction field. For a long time, research and development of electrochemical devices has progressed by increasing the functionality and sophistication of individual devices, but such an approach is becoming saturated. Advanced electrochemical devices require new science that is difficult to handle with conventional science. For example, in high-performance storage batteries for electric vehicles, various components are confined to the nano- to micro-scale, and it is essential to understand the complex phenomena occurred in the reaction field and establish how to control such phenomena. In high-speed water electrolysis and fuel cells, it is known that the bubbles generated by electrodes determine the performance, but even in such systems, no methodology has been established to understand the complex reaction field from material conversion to mass transfer. We propose to establish a cross-device science for the expansion of such reaction fields, and to promote the creation of new concepts of materials and the integration of technologies accumulated in each device, thereby promoting the efficiency and acceleration of materials development. Specifically, the following four R&D issues should be addressed.

• 1. Development of fundamental science for a cross-sectional understanding of the electricity-material-energy conversion reaction field

  Electrochemical devices contain many common factors even among devices with different purposes. However, materials and devices are currently being developed that are specialized and subdivided into individual systems. By constructing a science of the reaction field across devices, it is expected to create material concepts that cross over between devices and to create new materials and device development technologies. In particular, since the extension of reaction fields often involves harsh environments such as high current, high voltage, and high temperature, it is necessary to establish fundamental science to support the understanding of reaction fields in extreme environments. Specifically, understanding of interfacial phenomena consisting of heterogeneous materials, understanding of material states depending on the environmental characteristics of the reaction field (temperature, potential, pH), elucidation of electronic and ionic conduction mechanisms and search for new conduction mechanisms, should be addressed. Understanding reaction fields confined to the nanoscale, such as near electrode surfaces with complex nanostructures, is essential for the advancement of electrochemical devices. It is also necessary to develop operando measurement techniques, first-principles calculations, multiscale simulation methods, and data science methodologies to support the understanding of the reaction field. The methodologies constructed here will also contribute to the promotion of R&D topics 2, 3, and 4 listed below.

• 2. Development of materials that contribute to expanding the operating environment for electrochemical devices

  Research and development of new materials that realize a completely different operating environment from that of conventional devices or that can follow a wider range of operating environments than conventional devices is required. Specifically, there are R&D issues such as electrode materials, electrolyte materials, membrane materials, electrocatalysts, and conductive materials development that contribute to the expansion of temperature, electric potential, and pH (ion concentration), which are typical examples of the operating environment of electrochemical devices. These must be oriented toward low cost, overcoming resource constraints, and high stability with a view to mass implementation. Another challenge is to control not only electrochemical properties but also mechanical properties, as in the case of all solid-state batteries.

• 3. Creation of innovative electrochemical devices using novel materials

  The realization of a carbon-neutral society requires large-scale introduction of electrochemical systems and diversification of application areas. Based on the science of reaction fields and novel materials, we will promote the creation of devices in a rational and rapid manner. Energy applications using energy storage and electrolysis devices with low resource constraints, electrolytic synthesis of chemical products using CO2, alcohol synthesis for applications in the chemical and food fields, and development in emerging areas such as materials production (steel and cement), are also expected.

• 4. Development of electrochemical materials and device informatics

  With the diversification of electrochemical devices in the future, it will be necessary to establish technologies to optimize materials, device structures, and operating parameters as early as possible for each application. On the other hand, the electric-material energy conversion process has a very high degree of freedom in terms of components such as reaction substrates/carriers, electrode materials, and electrolyte materials. Informatics approach is required for rapid research and development of materials and device structures for such a complex reaction field with a huge number of combinations. In the short term, we will establish data-driven materials development technology (materials informatics) for electrochemical materials by utilizing large-scale data obtained through high-throughput calculations, high-throughput experiments, and advanced measurements. In the mid- to long-term, it is desirable to develop device informatics, in which the combination of heterogeneous materials and device design are performed by utilizing big data, with the aid of the cross-device science obtained in the Research Issue 1. For this purpose, it is necessary to enable more data accumulation and utilization, and it is required to construct a cross-device data utilization method for heterogeneous materials and devices.

The following promotion measures are proposed to effectively address the above R&D issues. Promote projects that address the pursuit of fundamental science across devices, materials exploration, and device development, and encourage new entrants from different fields. Strengthen the research support system to facilitate proof-of-concept of innovative materials and devices and establishment of standard evaluation technologies as an approach to lower the barriers to entry for newcomers from different fields. It is also considered necessary to establish a research center for the establishment of electrochemical material and device informatics technology, and to establish a consortium to promote social implementation of innovative electrochemical devices.