Bioelectrochemical production of hydrogen in an innovative pressure-retarded osmosis/microbial electrolysis cell system: experiments and modeling

Evaluation of different operational conditions in a microbial electrolysis cell inoculated with a pure culture of Shewanella oneidensis for hydrogen production

Hydrogen is a promising alternative to meet the world's energy demand in the future because of its energetic characteristics. Microbial electrolysis cell (MEC) produces hydrogen from organic matter using exoelectrogenic bacteria. Shewanella oneidensis stands out for having the capacity to produce hydrogen using different electron transfer mechanisms. The present research aims to evaluate the hydrogen production efficiency in a MEC inoculated with a pure culture of S. oneidensis in different operational conditions. Since the use of a catalyst accounts for most of the MEC cost, no catalyst was used for anode or cathode. Experiments were performed in semi-continuous and batch mode using different electrodes, voltages applied, and medium in aerobic and anaerobic conditions. The highest hydrogen production rate (HPR) was 0.107 m3 of H2/m3day obtained in a semi-continuous experiment using graphite plates and stainless steel electrodes. In batch experiments, a HPR occurred at 0.7 V, with a value of 0.048 m3 of H2/m3day versus 0.037 m3 of H2/m3day with 0.9 V. HPR was higher with carbon felt electrode (0.056 m3 of H2/m3day). However, current density dropped after 38 h, with carbon felt electrodes, and did not recover. Results of the present research showed that the MEC using a pure culture of S. oneidensis can be considered an alternative for hydrogen production without using a catalyst. Also, S. oneidensis produced hydrogen in both anaerobic and aerobic conditions with low methane production. Optimization can be proposed to improve hydrogen production based on the operational conditions tested in these experiments.

A modelling study of the spatially heterogeneous mutualism between electroactive biofilm and planktonic bacteria

Microbial cooperation widely exists in anaerobic reactors degrading complex pollutants, conventionally studied separately inside the biofilm or the planktonic community. Recent experiments discovered the mutualism between the planktonic bacteria and electroactive biofilm treating propionate, an end-product usually accumulated in anaerobic digesters. Here, a one-dimensional multispecies model found the preference on acetate-based pathway over the hydrogen-based in such community, evidenced by the fact that acetate-originated current takes 66% of the total value and acetate-consuming anode-respiring bacteria takes over 80% of the biofilm. Acetate-based anodic respiration most apparently influences biofilm function while propionate fermentation is the dominant planktonic bio-reaction. Additionally, initial planktonic propionate level shows the ability of coordinating the balance between these two extracellular electron transfer pathways. Increasing the propionate concentration from 2 to 50 mM would increase the steady hydrogen-originated current by 210% but decrease the acetate-originated by 26%, suggesting a vital influence of the planktonic microbial process to the metabolic balance in biofilm. Best strategy to promote the biofilm activity is to increase the biomass density and biofilm conductivity simultaneously, which would increase the current density by 875% without thickening the biofilm thickness or prolonging the growth apparently.

A review on self-sustainable microbial electrolysis cells for electro-biohydrogen production via coupling with carbon-neutral renewable energy technologies

Microbial electrolysis cell (MEC) technology is a promising bioelectrochemical hydrogen production technology that utilizes anodic bio-catalytic oxidation and cathodic reduction processes. MECs require a lower external energy input than water electrolysis; however, as they also require the application of external power sources, this inevitably renders MEC systems a less sustainable option. This issue is the main obstacle hindering the practical application of MECs. Therefore, this review aims to introduce a self-sustainable MEC technology by combining conventional MECs with advanced carbon-neutral technologies, such as solar-, microbial-, osmotic-, and thermoelectric-powers (and their combinations). Moreover, new approaches to overcome the thermodynamic barriers and attain self-sustaining MECs are discussed in detail, thereby providing a working principle, current challenges, and future perspective in the field. This review provides comprehensive insights into reliable hydrogen production as well as the latest trends towards self-sustainable MECs for practical application.

Microbial fuel cells: From fundamentals to applications. A review

In the past 10-15 years, the microbial fuel cell (MFC) technology has captured the attention of the scientific community for the possibility of transforming organic waste directly into electricity through microbially catalyzed anodic, and microbial/enzymatic/abiotic cathodic electrochemical reactions. In this review, several aspects of the technology are considered. Firstly, a brief history of abiotic to biological fuel cells and subsequently, microbial fuel cells is presented. Secondly, the development of the concept of microbial fuel cell into a wider range of derivative technologies, called bioelectrochemical systems, is described introducing briefly microbial electrolysis cells, microbial desalination cells and microbial electrosynthesis cells. The focus is then shifted to electroactive biofilms and electron transfer mechanisms involved with solid electrodes. Carbonaceous and metallic anode materials are then introduced, followed by an explanation of the electro catalysis of the oxygen reduction reaction and its behavior in neutral media, from recent studies. Cathode catalysts based on carbonaceous, platinum-group metal and platinum-group-metal-free materials are presented, along with membrane materials with a view to future directions. Finally, microbial fuel cell practical implementation, through the utilization of energy output for practical applications, is described.

Robotics in Lower-Limb Rehabilitation after Stroke

With the increase in the elderly, stroke has become a common disease, often leading to motor dysfunction and even permanent disability. Lower-limb rehabilitation robots can help patients to carry out reasonable and effective training to improve the motor function of paralyzed extremity. In this paper, the developments of lower-limb rehabilitation robots in the past decades are reviewed. Specifically, we provide a classification, a comparison, and a design overview of the driving modes, training paradigm, and control strategy of the lower-limb rehabilitation robots in the reviewed literature. A brief review on the gait detection technology of lower-limb rehabilitation robots is also presented. Finally, we discuss the future directions of the lower-limb rehabilitation robots.