AbstractFlash Joule heating (FJH) is an emerging and profitable technology for converting inexhaustible biomass into flash graphene (FG). However, it is challenging to produce biomass FG continuously due to the lack of an integrated device. Furthermore, the high-carbon footprint induced by both excessive energy allocation for massive pyrolytic volatiles release and carbon black utilization in alternating current-FJH (AC-FJH) reaction exacerbates this challenge. Here, we create an integrated automatic system with energy requirement-oriented allocation to achieve continuous biomass FG production with a much lower carbon footprint. The programmable logic controller flexibly coordinated the FJH modular components to realize the turnover of biomass FG production. Furthermore, we propose pyrolysis-FJH nexus to achieve biomass FG production. Initially, we utilize pyrolysis to release biomass pyrolytic volatiles, and subsequently carry out the FJH reaction to focus on optimizing the FG structure. Importantly, biochar with appropriate resistance is self-sufficient to initiate the FJH reaction. Accordingly, the medium-temperature biochar-based FG production without carbon black utilization exhibited low carbon emission (1.9 g CO2-eq g−1 graphene), equivalent to a reduction of up to ~86.1% compared to biomass-based FG production. Undoubtedly, this integrated automatic system assisted by pyrolysis-FJH nexus can facilitate biomass FG into a broad spectrum of applications.

Graphene is widely applied in many important technologies, with demand projected to grow exponentially. Conventional graphene production approaches that use natural/artificial graphite are expensive and energy and chemical intensive, resulting in a significant environmental footprint. The recent flash Joule heating (FJH) technology that can produce flash graphene (FG) from carbon-rich waste materials has been proposed as a cleaner production process, but the quality of FG made from biomass waste via FJH and the overall sustainability of the process remain unclear. Here we conduct lab-scale experiments to fill these knowledge gaps. We show that biomass waste-derived FG shows excellent thermal and electrical conductivity, and the FJH process results in a more than 10-fold decrease in life-cycle environmental impacts including carbon emissions and freshwater use relative to the conventional approaches. The FJH process is also cost effective, with the biomass waste-derived FG being much cheaper than graphite-based graphene. Our study identifies circular and sustainable opportunities for future graphene production.

Many research fields need special high-voltage pulses in pulsed power applications, which are different from typical rectangular pulses. In this paper, a high-voltage waveform modulator of two methods using a solid-state Marx generator has been developed and tested. Instead of manufacturing a generator with a specialized structure, the modulator can control a general Marx generator by low-voltage programmable logic devices to produce an irregular but controllable high-voltage triangular pulse with pulse length of ~4.5 μs and peak voltage of ~123 kV.

Dielectric barrier discharge (DBD) is used in plasma technology with wide applications, such as ozone generation, depollution of gas stream and surface treatment of plastics. Commonly used power supplies for DBD generate sinusoidal voltages with frequency up to 100 kHz. Recent research shows that apart from a primary discharge occurring at the rising front or during the pulse top, a secondary discharge occurs at the end of the falling voltage flank when unipolar square pulses are used. This excitation method of DBDs improves energy efficiency significantly compared with sinusoidal excitation.In this paper, an all-solid-state Marx generator that can generate nearly rectangular pulses with a DBD load is proposed. It operates at an output voltage of 30 kV, a repetition frequency of 1 kHz and 1 kV DC input voltage successfully. Both the rise and fall times are less than 200 ns, and a maximum pulse-width of 1 us is obtained. A transformer isolated gate drive circuit is employed.This prototype has been applied in gas treatment research using DBD. Preliminary experimental results show that it is able to deliver almost rectangular voltage pulse to resistive load and capacitive load. When driving a DBD load, it can output large current at the rising of a pulse.

This paper proposes a novel bipolar high-voltage Marx pulse current generator for inductive load. The paper first analyzes the feasibility and design parameters of the proposed design, and then elaborates the structure design and optimization. IGBT modules build up the 10-stage Marx adder, and the capacitor in each stage is charged by series-parallel resonant voltage converter. A novel compensation strategy is proposed for the energy loss of the inductive load and the characteristics of switching devices. 1 kA peak current bipolar pulse is achieved with 300 ns rise/fall time and 1.5 μs flattop on a 2 μH inductor. Compared with traditional PFN current generator, this solid-state pulse current generator has similar performance while being easier to adjust and is more compact in shape.

A newly developed bipolar high-voltage pulse adder with a novel control method is proposed in this paper. The system adopts modularization design; typical full-bridge semiconductor structure is the basis of each stage. Owe to the phase-shifted control method, the pulse adder has the ability of generating fast narrow bipolar high-voltage pulses. The flexible operation of full-bridge units is fully utilized to solve the problems caused by stray capacitance.