Zalacca is one of the fruits that has various benefits. This fruit has properties as a guardian of the body’s health, improve memory, increase stamina, and has benefits for treating nearsightedness and constipation.  Aside from the fruit, zalacca skin also has benefits. According to research conducted by ITB students, salak skin can overcome diabetes. This is evidenced by the blood sugar of experimental rats decreased from 210 to 100 after drinking bark extract. 
However, the benefits of zalacca are not limited to health, zalacca also has a function in the energy sector as a raw material for producing activated carbon. Activated carbon is a material that has a very high absorption (adsorption) ability. This material is like a sponge that is able to absorb the water around it, it’s just that activated carbon is not used to absorb water but absorbs impurities and energy.
Figure 1. Example of the application of activated carbon in a methyl blue solution, the left beaker is not given activated carbon while the right beaker is given activated carbon 
This ability is caused by this material having microscopic pores so that it has a very large surface area. The greater the surface area of a material, the greater the ability of adsorption. The high level of adsorption means that the material is able to store something in large quantities.
The superiority of the activated carbon material makes it a good compiler for capacitors. Capacitors are devices used to store energy in electric charges. The function of this capacitor is similar to a battery which also functions as an energy storage. In addition, the capacitors also have other functions of interference filtering devices on the radio transmitter, preventing an electric jump, as a link between low-level amplifiers to high levels, etc. So, the benefits of zalacca skin are the raw material for activated carbon, which is the material making up capacitors and these capacitors function to store energy. 
Figure 2. Example of a capacitor
This is consistent with the research journal chaired by Ratna Frida Susanti from Parahyangan University, Bandung. This journal discusses the manufacture of activated carbon from salak skin as a compiler for capacitors using catalized hydrothermal carbonization technology with a citric acid catalyst. This journal was released in February 2019 on Springer Link after it was previously presented at the 2017 MRS-INA C&C on October 8-12, 2018.
This research is motivated by the shortcomings of Electric Double-Layer Capacitor (EDLC) devices which have high power density, recycling capacity, and life cycle, but have low energy density. And also Lithium-ion battery (LIB) devices which have high energy density, but low power density and life cycle. In order to produce a device that includes the positive properties of the two devices, a hybrid energy storage device called a Lithium-ion Capacitor was developed(LIC). LIC is a hybrid of supercapacitor and LIB material, with battery anodes and cathode capacitors. The cathode from LIC is based on activated carbon because activated carbon is used as an inexpensive, abundant, non-toxic electrode, good chemical stability, excellent electronic conductivity and wide operating temperatures. 
This research uses hydrothermal carbonization technology (HTC), which is a thermochemical process technology that converts wet biomass waste into coal-like material with high carbon content called hydrochar .  HTC technology that uses catalysts in the process is called catalized hyrothermal carbonization (CHC). The function of the catalyst is to improve the material performance of the HTC process so that hydrochar is createdhigh quality. Meanwhile, the advantages of implementing this HTC technology are environmentally friendly, operating in moderate temperatures, able to process high-humidity biomass materials without complicated and expensive processes. In addition, product size and shape can be regulated and produce less greenhouse gases. 
Figure 3. General concept of HTC technology, biomass is treated with subcritical water to produce hydrochar
The research procedure was carried out at a pressure of 5 MPa for 5 hours in subcritical water, with citric acid as an experimental catalyst at temperatures between 200-250 ° C. After going through the HTC process, the hydrochar activation process is carried out using KOH. KOH is used because KOH is the best activated carbon activator based on previous experiments. The form of hydrochar and activated carbon was measured by Scanning Electron Microscope (SEM) and the chemical changes were measured by Fourier transform infrared spectroscopy (FTIR), while the surface and pore size were measured by nitrogen adsorption at 77.35K. The electrochemical performance of activated carbon from salak skin and commercial activated carbon from coin cells was evaluated by CV, GCD, and EIS. 
The results of this study indicate that the presence of a citric acid catalyst in the HTC process creates activated carbon with a greater surface area and the intensity of oxygenated group capacitance in activated carbon catalysts is stronger. When compared, the capacitance of activated carbon is catalyst 100 cycles greater than non-catalyzed activated carbon. In addition, it was also shown that activated carbon from salak peel has better material properties and electrochemical performance than commercial activated carbon. This shows the potential of zalacca skin as a pioneer in the activated carbon industry. 
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- Susanti, RF, Arie, AA, Kristianto, H. et al. (2019). Activated carbon from citric acid catalyzed hydrothermal carbonization and chemical activation of salacca peel as potential electrode for lithium ion capacitor’s cathode. Ionics 25: 3915. https://doi.org/10.1007/s11581-019-02904-x
- Putra, Herlian & Dewi, Kania & Pasek, Ari & Damanhuri, Enri. (2017). Hydrothermal carbonization of biomass waste by using a stirred reactor: an initial experimental results. Reactor. 16. 212. 10.14710 / reactor. 16.4.212-217.
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