# Technology-Economy-Policy: Biochar in the Low-Carbon Energy Transition--A Review
## 3 Biochar  
Bioproducts are environmentally friendly innovative products that can be obtained from biomass resources, offering sustainable solutions in various industries [7]. Currently, there is a wide range of bioproducts, such as bioplastics, biocomposites, and biofuels, etc., that have reached the commercialization phase and have shown successful results. An important branch of biomass products is biochar [38]. Biochar is a carbon-rich bioproduct formed by heating organic matter in a low-oxygen environment [39] or under anaerobic conditions [40]. Biochar is a technical term. The literature of the subject reports its various definitions. [PERSON] and [PERSON] [41; 42] define biochar as \"a product rich in carbon (C)\". According to [PERSON] et al. [43], biochar is a \"porous solid carbon product\". [PERSON] et al. [44] described biochar as \"biomass that has been pyrolyzed in a zero- or low-oxygenenvironment applied to soil at a specific location\". The definitions of biochar in the scientific literature are directly or indirectly related to its production process and potential application. Biochar is a carbon-rich product derived from the pyrolysis of solid biomass waste [41]. Biochar is a unique material with enormous potential. It is considered a very important tool for environmental management [42; 43; 44; 45; 46; 47; 48; 49]. For thousands of years, charcoal has been one of the basic materials in the development of civilization [50]. Over the past few years, there has been tremendous progress in the field of biochar, both in science and industry, and its potential for use has increased interest in its beneficial applications in carbon sequestration, soil fertility improvement, pollution remediation, wastewater treatment, thermal and metallurgical purposes, and the metallurgical industry, etc. [51]. Recent studies suggest that biochar can be successfully used in both soil and non-soil applications, as it has the potential to combat climate change and maintain environmental sustainability [45]. The possibilities of using different origins of biochar to achieve carbon neutrality are presented in the diagram below (Figure 1). The structure of biochar is characterized by a porous and complex composition [52]. Biochar is known for its significant porosity, characterized by a diverse range of sizes and distribution of pores [53]. It consists of a network of carbon-rich particles formed during the carbonization of biomass. This porosity increases the ability of biochar to retain water, nutrients, and other substances [54]. Indeed, when biomass undergoes pyrolysis, the dehydration process leads to the loss of water and the release of volatile components  
Figure 1: Different applications of biochar for carbon neutrality. Own elaboration. from the carbon matrix, which contributes to the formation of the pore structure of the biochar. These pores are divided into three groups: micropores (<2 nm), mesopores (2-50 nm), and macropores (>50 nm) [55]. Porosity is a key factor when biochar is used for applications other than energy production. For example, as sorbents or fertilizers, the porosity of biochars significantly affects their effect on the biological, chemical, and physical properties of the soil [56]. In addition, biochar has a significant surface area due to its porous nature [55]. This property is a key attribute of biochar in chemical reactions, adsorption, and interactions with other substances. At the microscopic level, biochar consists of a mixture of amorphous carbon, microcrystalline structures, and residual organic matter [57]. These structures contribute to the physical properties and reactivity of biochar. [PERSON] et al. show that [58] the surface of biochar can contain functional groups such as hydroxyl, carboxyl, and phenolic groups, which are responsible for various chemical behaviors and interactions, such as increasing their sorption properties.