Modular Flow Reactors for Valorization of Kraft Lignin and Low???Voltage Hydrogen Production

Recent studies have found that green hydrogen production and biomass utilization technologies can be combined to efficiently produce both hydrogen and value-added chemicals using biomass as an electron and proton source. However, the majority of them have been limited to proof-of-concept demonstrations based on batch systems. Here the authors report the design of modular flow systems for the continuous depolymerization and valorization of lignin and low-voltage hydrogen production. A redox-active phosphomolybdic acid is used as a catalyst to depolymerize lignin with the production of aromatic compounds and extraction of electrons for hydrogen production. Individual processes for lignin depolymerization, byproduct separation, and hydrogen production with catalyst reactivation are modularized and integrated to perform the entire process in the serial flow. Consequently, this work enabled a one-flow process from biomass conversion to hydrogen gas generation under a cyclic loop. In addition, the unique advantages of the fluidic system (i.e., effective mass and heat transfer) substantially improved the yield and efficiency, leading to hydrogen production at a higher current density (20.5 mA cm???2) at a lower voltage (1.5 V) without oxygen evolution. This sustainable eco-chemical platform envisages scalable co-production of valuable chemicals and green hydrogen for industrial purposes in an energy-saving and safe manner

Bias-free solar hydrogen production at 19.8???mA???cm???2 using perovskite photocathode and lignocellulosic biomass

Solar hydrogen production is one of the ultimate technologies needed to realize a carbon-neutral, sustainable society. However, an energy-intensive water oxidation half-reaction together with the poor performance of conventional inorganic photocatalysts have been big hurdles for practical solar hydrogen production. Here we present a photoelectrochemical cell with a record high photocurrent density of 19.8???mA???cm???2 for hydrogen production by utilizing a high-performance organic???inorganic halide perovskite as a panchromatic absorber and lignocellulosic biomass as an alternative source of electrons working at lower potentials. In addition, value-added chemicals such as vanillin and acetovanillone are produced via the selective depolymerization of lignin in lignocellulosic biomass while cellulose remains close to intact for further utilization. This study paves the way to improve solar hydrogen productivity and simultaneously realize the effective use of lignocellulosic biomass

Electrochemical Oxidation of Biomass for Solar Fuel Production

Solar-to-chemical energy conversion, so-called artificial photosynthesis has received great attentions to address modern energy and environmental problems as it allows carbon-neutral production and the use of various chemical compounds, such as hydrogen, CO, and formate. Despite huge efforts made for decades, it still remains promising but premature for practical implementation due to low efficiency and stability of photosynthetic devices/materials. This is because of the slow and harsh water oxidation process, which can act as a rate-determining step for the overall reactions and lower the stability of photosynthetic devices. To address such problems, here, we report the coupling of photocatalytic reduction reactions for the synthesis of target chemicals with the electrochemical oxidation of biomass. By utilizing catalytic redox mediators, electrons were readily extracted from electrocatalytic oxidation and depolymerization of biomasses for electrochemical and photoelectrochemical hydrogen production. As a result, we could significantly reduce the oxidation potential for the extraction of electrons by several hundreds of mV and improve the performance of the devices in terms of kinetics and stability by employing biomass as a source of electrons instead of water. The catalytic redox mediators exhibited excellent stability in repeated biomass oxidation. We believe that the present study can provide insights for design and fabrication of artificial photosynthetic devices for practical application

Cobalt polyoxometalate-derived CoWO4 oxygen-evolving catalysts for efficient electrochemical and photoelectrochemical water oxidation

Highly efficient water-oxidation catalysts (WOCs) were readily prepared through the simple heat treatment of cobalt-containing polyoxometalate [Co4(H2O)2(PW9O34)2]10− (POM). The annealing of soluble POM molecules at high temperatures in air led to the formation of insoluble nanoparticles, of which the crystal structure and catalytic activity can be controlled by the annealing temperature. POMs were converted to amorphous and crystalline CoWO4 nanoparticles when annealed at 400 and 500 ??C, respectively. Interestingly, amorphous CoWO4 nanoparticles exhibited excellent catalytic activity near the neutral pH of pH 8.0, making them superior to both pristine POM and POM-derived crystalline CoWO4 nanoparticles. X-ray absorption and photoelectron spectroscopies combined with density functional theory (DFT) calculations revealed that their outstanding performance was resulted from the generation of large amounts of oxygen vacancies upon annealing, leading to the optimum distance between the nearest Co ions for the Langmuir-Hinshelwood (LH) mechanism. Based on these findings, we could readily immobilize CoWO4-based WOCs on the surfaces of various electrodes for efficient electrochemical and photoelectrochemical water oxidation through the annealing of POMs pre-adsorbed onto the desired electrode surface. This study may provide insights not only for the synthesis of efficient electrocatalysts derived from POMs but also for their immobilization onto the desired electrode surface for practical applications