In order to achieve a carbon-efficient circular economy, a paradigm shift is required to valorize carbon dioxide (CO2) and organic wastes into value-added products. Among others, microbial electrosynthesis (MES) and electrofermentation (EF) technologies have shown the potential to contribute to the circular carbon economy. Besides carbon conversion, both technologies can be applied to store excess green energy in the form of valuable transportable chemicals. This article sheds light on the current status of MES and EF technologies by covering the most important literature from the last two years. Recent progress on reactor design and process optimization, scale-up attempts, and a summary of ongoing or completed technology-oriented research projects over the recent years are presented. Furthermore, the key challenges and future research perspectives desired to enable the implementation of the MES technology are also discussed. 

Technological progress and readiness level of microbial electrosynthesis and electrofermentation for carbon dioxide and organic wastes valorization

Scale-up of the bioelectrochemical system: Strategic perspectives and normalization of performance indices.

Porous polyurethane particles enhanced the acetate production of a hydrogen-mediated microbial electrosynthesis reactor

A 20 L electrochemical continuous stirred-tank reactor for high rate microbial electrosynthesis of methane from CO2

Advances in cathode designs and reactor configurations of microbial electrosynthesis systems to facilitate gas electro-fermentation.

An electrolytic-hydrogen-fed moving bed biofilm reactor for efficient microbial electrosynthesis of methane from CO2

The recovery of noble metal ions from wastewater without energy consumption is of utmost importance. Herein, a methanol-Ag+ coupled redox fuel cell (CRFC) was developed to realize silver removal and electricity generation simultaneously. In this system with alkaline methanol as fuel on the anode, Ag+ in catholyte was reduced. The highest open circuit voltage of 1.28 V and maximum power density of 17.4 W·m−2 were achieved at 0.1 mol·L−1 Ag+ (pH=1.1). More than 90% Ag+ can be removed in 6 h, and over 60% of cathodic efficiency was achieved simultaneously when using Ag+ as electron acceptors. Morphology analysis showed that dendritic Ag particles were loosely deposited on the cathode after 2 h operation. The size of the silver dendrites increased with Ag+ concentration increase. Eventually, a fed-batch mode was conducted to confirm that either the Ag+ is efficiently reduced or the energy in chemicals has been sustainably retrieved in electricity. 

Incorporation of silver recovery with electricity generation through methanol-Ag+ coupled redox fuel cell

BACKGROUND The availability of highly active, low-cost and stable oxygen reduction reaction (ORR) electrocatalysts remains a barrier to the development of energy techniques. This study presents molybdenum trioxide/reduced graphene oxide (MoO3/rGO) composite as an effective electrocatalytic material for ORR. RESULTS The nanosized MoO3 particles loaded on rGO as an efficient ORR catalyst was prepared via a two-step method. The MoO3(0.1)/rGO nanocomposite showed the highest content of Mo6+ and rGO carbon among rGO and MoO3/rGO. The MoO3(0.1)/rGO showed the highest limiting current density of −3.04 mA cm−2 at 0.2 V versus reversible hydrogen electrode, which was comparable to the commercial 10% Pt/C in the present work. The electron transfer number of 2.74 on MoO3(0.1)/rGO indicated ORR selectivity towards the four-electron pathway was not very high. The electrochemical active surface area of the MoO3(0.1)/rGO nanocomposite was 9.94 cm2, which was about twice the commercial 10% Pt/C. The small Tafel slope of 57.56 mV dec−1 confirms the high ORR activity of the MoO3(0.1)/rGO catalyst. The MoO3(0.1)/rGO also showed good stability under alkaline conditions and better methanol tolerance compared to the commercial 10% Pt/C. CONCLUSION The increased activity of the MoO3(0.1)/rGO composite may be attributed to the higher content of Mo6+ and rGO carbon in the catalyst. Performance of the catalysts may be further improved by optimizing the experimental conditions. The synthesized MoO3/rGO composite is a potential alternative electrocatalyst for ORR. © 2022 Society of Chemical Industry (SCI). 

Amrendra Kumar Singh

Papers

An electrolytic-hydrogen-fed moving bed biofilm reactor for efficient microbial electrosynthesis of methane from CO2

An electrolytic-hydrogen-fed moving bed biofilm reactor for efficient microbial electrosynthesis of methane from CO2

Incorporation of silver recovery with electricity generation through methanol-Ag+ coupled redox fuel cell

Enhanced electrocatalytic activities of <scp> MoO <sub>3</sub> </scp> / <scp>rGO</scp> nanocomposites for oxygen reduction reaction