# Technology-Economy-Policy: Biochar in the Low-Carbon Energy Transition--A Review
## 6 Economy: Application of Biochar
### Application of Biochar in the Renewable Energy Sector
#### 6.1.5 Biochar as a Building Material to Achieve Carbon Neutrality  
The demand for construction materials continues to grow due to global population growth and infrastructure development. Scientific sources report that about 40% of total CO2 emissions come from construction work. Cement production generates 36% of total CO2 emissions [45]. During the construction of buildings, 70% of CO2 emissions come from the use of cement, and the remainder from the transportation of raw materials and aggregate production [45]. Therefore, to achieve carbon neutrality, it is necessary to develop building materials with a smaller or negligible carbon footprint. Biochar, as a material with a negative carbon footprint, has demonstrated its use as a carbon-neutral/negative substitute for cement or aggregate [192]. Fine-grained biochar can be used as a cement material, while coarse  
Figure 3: An example of the process of making and using biochar in supercapacitors [188]. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Application/Device** & **Biochar Function** & **Modification** & **Performance/Parameters** & **Ref.** \\ \hline \multirow{4}{*}{Lithium-ion battery} & \multirow{2}{*}{Anode} & Pure biochar & Enhanced Li\({}^{+}\) transfer & [184] \\ \cline{3-5}  & & Biochar with Ni and & Higher reusability and & \\  & & Sn & discharge capacity & [185] \\ \cline{2-5}  & & Fe\({}_{3}\)C–biochar & & \\  & & composite & 555 mAh/g after 250 cycles & [186] \\ \hline \multirow{2}{*}{Zinc–air battery} & \multirow{2}{*}{Cathode} & KCl-activated & Higher capacitance and peak & \\  & & biochar & power density vs. Pt/C & [187] \\ \hline Solar absorber coatings & Pigment material & Pure biochar & Reduced reflectance & [188] \\ \hline Dye-sensitized solar cell (DSSC) & Catalyst (counter electrode) & Biochar replacing Pt & Effective Pt replacement & [189] \\ \hline Electrochemical & \multirow{2}{*}{Electrode (EDLC)} & High-temperature & High conductivity and & \\  & & pyrolyzed biochar & graphite-like structure & [190] \\ \hline Composite supercapacitor & Electrode & Biochar with MnO2, & Increased capacitance and & \\  & & NiO, and polyaniline & cycling stability & [191] \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Applications of biochar in energy storage devices along with corresponding performance parameters. grained biochar can replace aggregate in concrete. Biochar has an affinity with cement, asphalt, and polymeric materials due to its porous nature and functional surface, which is where chemical reactions take place. The use of biochar as an additive to building materials offers a number of benefits, such as hygrothermal regulation, improved indoor air quality, self-repairing ability, sound insulation, electromagnetic shielding, and the immobilization of pollutants. Adding 1% of biochar to a cement matrix can increase its compressive strength by up to 9% [193]. The large surface area, porosity, and surface features of biochar increase water retention and CO\({}_{2}\) storage capacity and can promote the use of biochar as a building material through internal hardening and carbonation [194; 195; 196]. Adding 4% of biochar to cement stores 0.12 kg of CO\({}_{2}\), and supplementing cement with 8% of biochar reduces CO\({}_{2}\) emissions by up to 15% compared to Portland cement. The use of biochar as a filler material with a negative carbon footprint can improve the properties of cement-based composites and promote environmental sustainability. Adding biochar to construction materials retains water, which promotes internal curing, facilitates the hydration of biochemical composites, and ensures long-term durability [197] (Figure 4). [PERSON] et al. reported that fine biochar can replace cement due to its lightness and high strength and can be used in the production of ultra-high-performance concrete [198]. Supplementing with 2 and 5% of biochar reduced the shrinkage of the calcined marine clay-based concrete to 21 and 32%, respectively.