Effects of Nanoporous Carbon Derived from Microalgae and Its CoO Composite on Capacitance

An integrated smartphone-based electrochemical detection system for highly sensitive and on-site detection of chemical oxygen demand by copper-cobalt bimetallic oxide-modified electrode

A portable and integrated electrochemical detection system has been constructed for on-site and real-time detection of chemical oxygen demand (COD). The system mainly consists of four parts: (i) sensing electrode with a copper-cobalt bimetallic oxide (CuCoOx)-modified screen-printed electrode; (ii) an integrated electrochemical detector for the conversion, amplification, and transmission of weak signals; (iii) a smartphone installed with a self-developed Android application (APP) for issuing commands, receiving, and displaying detection results; and (iv) a 3D-printed microfluidic cell for the continuous input of water samples. Benefiting from the superior catalytic capability of CuCoOx, the developed system shows a high detection sensitivity with 0.335 μA/(mg/L) and a low detection limit of 5.957 mg/L for COD determination and possessing high anti-interference ability to chloride ions. Moreover, this system presents good consistency with the traditional dichromate method in COD detection of actual water samples. Due to the advantages of cost effectiveness, portability, and point-of-care testing, the system shows great potential for water quality monitoring, especially in resource-limited remote areas.

Electrochemical Performance of Nitrogen Self-Doping Carbon Materials Prepared by Pyrolysis and Activation of Defatted Microalgae

Pyrolysis and activation processes are important pathways to utilize residues after lipid extraction from microalgae in a high-value way. The obtained microalgae-based nitrogen-doped activated carbon has excellent electrochemical performance. It has the advantage of nitrogen self-doping using high elemental nitrogen in microalgae. In this study, two kinds of microalgae, Nanochloropsis and Chlorella, were used as feedstock for lipid extraction. The microalgae residue was firstly pyrolyzed at 500 °C to obtain biochar. Then, nitrogen-doped activated carbons were synthesized at an activation temperature of 700-900 °C with different ratios of biochar and KOH (1:1, 1:2, and 1:4). The obtained carbon materials presented rich nitrogen functional groups, including quaternary-N, pyridine-N-oxide, pyrrolic-N, and pyridinic-N. The nitrogen content of microalgae-based activated carbon material was up to 2.62%. The obtained materials had a specific surface area of up to 3186 m2/g and a pore volume in the range of 0.78-1.54 cm3/g. The microporous pore sizes of these materials were distributed at around 0.4 nm. Through electrochemical testing such as cyclic voltammetry and galvanostatic charge-discharge of materials, the materials exhibited good reversibility and high charge-discharge efficiency. The sample, sourced from microalgae Chlorella residue at activation conditions of 700 °C and biochar/KOH = 1:4, exhibited excellent endurance of 94.1% over 5000 cycles at 2 A/g. Its high specific capacitance was 432 F/g at 1 A/g.

Enhanced electrochemical performance of the cobalt chloride carbonate hydroxide hydrate via micromorphology and phase transformation

Micromorphology and conductivity are two vital factors for the practical capacitance of the electrode materials for supercapacitors. In this work, a novel two-step electrochemical activation method involving a cyclic voltammetry (CV) treatment within 0-0.7 V followed by a CV treatment within -1.2-0 V is explored to induce the micromorphology and phase transformation of the cobalt chloride carbonate hydroxide hydrate (CCCH) nanoneedle arrays. The first-step activation transforms the CCCH to Co(OH)₂ and then the reversible transformation between Co(OH)₂ and CoOOH generates plenty of pores in the sample, thereby increasing the specific capacitance from 0.54 to 1.74 F cm^-2 at the current density of 10 mA cm^-2. The second-step activation inducing the reversible transformation between Co(OH)₂ and Co not only endows the final sample with a nanosheets-assembled fasciculate structure but also decreases the internal resistance via generating Co⁰ in the final sample (CCCH-P75N50). Consequently, the CCCH-P75N50 shows a high specific capacitance of 3.83 F cm^-2 at the current density of 10 mA cm^-2. Besides, the aqueous asymmetric supercapacitor assembled with CCCH-P75N50 and commercial conductive carbon cloth (CC) delivers a high energy density of 2.75 mWh cm^-3 at a power density of 37.5 mW cm^-3. This work provides a novel, facile and promising method to optimize the micromorphology and conductivity of Co-based electrodes.

A state-of-the-art review on algae pyrolysis for bioenergy and biochar production

Algae, as a feedstock with minimum land footprint, is considered a promising biomass for sustainable fuels, chemicals, and materials. Unlike lignocellulosic biomass, algae consist mainly of lipids, carbohydrates, and proteins. This review focusses on the bio-oil and biochar co-products of algae-pyrolysis and presents the current state-of-the-art in the pyrolysis technologies and key applications of algal biochar. Algal biochar holds potential to be a cost-effective fertilizer, as it has high P, N and other nutrient contents. Beyond soil applications, algae-derived biochar has many other applications, such as wastewater-treatment, due to its porous structure and strong ion-exchange capacity. High specific capacitance and stability also make algal biochar a potential supercapacitor material. Furthermore, algal biochar can be great catalysts (or catalyst supports). This review sheds light on a wide range of algae-pyrolysis related topics, including advanced-pyrolysis techniques and the potential biochar applications in soil amendment, energy storage, catalysts, chemical industries, and wastewater-treatment plants.