Shigenori Fujikawa

Climate change caused by the emission of greenhouse gases into the atmosphere is a major concern for our society. Carbon dioxide (CO₂) capture from the air (Direct Air Capture, DAC) is one of several negative emission technologies that are expected to keep global warming below 1.5°C.

   CO₂ capture using permselective membranes is advantageous because of its smaller and simpler design. Unfortunately, its efficiency is not satisfactory for practical operation of the DAC. Poly(dimethylsiloxane) (PDMS) is known to have high CO₂ permeability. We have developed defect-free, free-standing nanomembranes of PDMS, and the developed 34 nm-thick nanomembranes exhibit world-high CO₂ permeance1 with reasonable CO₂/N₂ selectivity.^[1] The separation is achieved even at atmospheric CO₂ concentration (about 400 ppm). Based on these achievements, we first proposed the concept of membrane-based DAC (m-DAC),^[2] which was previously considered impossible.^[3] In nanometer thick membranes, the interaction between the gas molecules and the membrane surface has a significant effect on the performance of the entire membrane. We observed anisotropic gas permeance behavior depending on the direction of feed gas introduction to the membrane faces.^[4] This finding provides new aspect for membrane design. Currently, our current efforts are also being focused on developing a continuous process from DAC to the production of methane and carbon monoxide through collaborative research activities.^[5] A key challenge in implementing a combined m-DAC and chemical reduction system is the presence of impurity gases, such as nitrogen (N₂) and oxygen (O₂), in the permeate gas. While the presence of N₂ only reduces the CO₂ reduction reaction rate due to the dilution effect, the presence of O₂ is detrimental to the reaction as it is preferentially reduced. We have recently reported CO₂/O₂ separation by magnetic mixed matrix membranes (MMMs) with magnetic nanoparticle (MNP) fillers in polymer matrices, which exhibit room temperature trapping of gaseous O₂ within the membrane to achieve high CO₂/O₂ selectivities.^[6]

Dr. Shigenori Fujikawa is Distinguished Professor of the International Institute for Carbon-Neutral Energy Research (WPI-I2CNER) and Director of the Research Center for Negative Emissions Technologies at Kyushu University. He received his Ph.D. degree from Kyushu University (1999). He did his postdoctoral research at Yale University as a JSPS Postdoctoral Fellow and at RIKEN as a special postdoctoral researcher. He has led his independent research group at RIKEN from 2004 to 2012 before joining the Kyushu University faculty in 2012. His research focuses on CO2 separation nanomembranes, free-standing thin films, and direct air capture technologies.