Yilun Li

Flexible Boron-Doped Laser-Induced Graphene Microsupercapacitors

Heteroatom-doped graphene materials have been intensely studied as active electrodes in energy storage devices. Here, we demonstrate that boron-doped porous graphene can be prepared in ambient air using a facile laser induction process from boric acid containing polyimide sheets. At the same time, active electrodes can be patterned for flexible microsupercapacitors. As a result of boron doping, the highest areal capacitance of as-prepared devices reaches 16.5 mF/cm(2), 3 times higher than nondoped devices, with concomitant energy density increases of 5-10 times at various power densities. The superb cyclability and mechanical flexibility of the device are well-maintained, showing great potential for future microelectronics made from this boron-doped laser-induced graphene material.

High-Performance Hydrogen Evolution from MoS2(1-x) P(x) Solid Solution.

A MoS2(1-x) P(x) solid solution (x = 0 to 1) is formed by thermally annealing mixtures of MoS2 and red phosphorus. The effective and stable electrocatalyst for hydrogen evolution in acidic solution holds promise for replacing scarce and expensive platinum that is used in present catalyst systems. The high performance originates from the increased surface area and roughness of the solid solution.

High-Performance Pseudocapacitive Microsupercapacitors from Laser-Induced Graphene.

All-solid-state, flexible, symmetric, and asymmetric microsupercapacitors are fabricated by a simple method in a scalable fashion from laser-induced graphene on commercial polyimide films, followed by electrodeposition of pseudocapacitive materials on the interdigitated in-plane architectures. These microsupercapacitors demonstrate comparable energy density to commercial lithium thin-film batteries, yet exhibit more than two orders of magnitude higher power density with good mechanical flexibility.

Lithium Batteries with Nearly Maximum Metal Storage

The drive for significant advancement in battery capacity and energy density inspired a revisit to the use of Li metal anodes. We report the use of a seamless graphene-carbon nanotube (GCNT) electrode to reversibly store Li metal with complete dendrite formation suppression. The GCNT-Li capacity of 3351 mAh g-1GCNT-Li approaches that of bare Li metal (3861 mAh g-1Li), indicating the low contributing mass of GCNT, while yielding a practical areal capacity up to 4 mAh cm-2 and cycle stability. A full battery based on GCNT-Li/sulfurized carbon (SC) is demonstrated with high energy density (752 Wh kg-1 total electrodes, where total electrodes = GCNT-Li + SC + binder), high areal capacity (2 mAh cm-2), and cyclability (80% retention at >500 cycles) and is free of Li polysulfides and dendrites that would cause severe capacity fade.

In Situ Formation of Metal Oxide Nanocrystals Embedded in Laser-Induced Graphene

Hybrid materials incorporating the advantages of graphene and nanoparticles have been widely studied. Here we develop an improved cost-effective approach for preparation of porous graphene embedded with various types of nanoparticles. Direct laser scribing on metal-complex-containing polyimide film leads to in situ formation of nanoparticles embedded in porous graphene. These materials are highly active in electrochemical oxygen reduction reactions, converting O2 into OH(-), with a low metal loading of less than 1 at. %. In addition, the nanoparticles can vary from metal oxide to metal dichalcogenides through lateral doping, making the composite active in other electrocatalytic reactions such as hydrogen evolution.

Asphalt-derived high surface area activated porous carbons for carbon dioxide capture.

Research activity toward the development of new sorbents for carbon dioxide (CO2) capture have been increasing quickly. Despite the variety of existing materials with high surface areas and high CO2 uptake performances, the cost of the materials remains a dominant factor in slowing their industrial applications. Here we report preparation and CO2 uptake performance of microporous carbon materials synthesized from asphalt, a very inexpensive carbon source. Carbonization of asphalt with potassium hydroxide (KOH) at high temperatures (>600 °C) yields porous carbon materials (A-PC) with high surface areas of up to 2780 m(2) g(-1) and high CO2 uptake performance of 21 mmol g(-1) or 93 wt % at 30 bar and 25 °C. Furthermore, nitrogen doping and reduction with hydrogen yields active N-doped materials (A-NPC and A-rNPC) containing up to 9.3% nitrogen, making them nucleophilic porous carbons with further increase in the Brunauer-Emmett-Teller (BET) surface areas up to 2860 m(2) g(-1) for A-NPC and CO2 uptake to 26 mmol g(-1) or 114 wt % at 30 bar and 25 °C for A-rNPC. This is the highest reported CO2 uptake among the family of the activated porous carbonaceous materials. Thus, the porous carbon materials from asphalt have excellent properties for reversibly capturing CO2 at the well-head during the extraction of natural gas, a naturally occurring high pressure source of CO2. Through a pressure swing sorption process, when the asphalt-derived material is returned to 1 bar, the CO2 is released, thereby rendering a reversible capture medium that is highly efficient yet very inexpensive.

Preparation of Three-Dimensional Graphene Foams Using Powder Metallurgy Templates

A simple and scalable method which combines traditional powder metallurgy and chemical vapor deposition is developed for the synthesis of mesoporous free-standing 3D graphene foams. The powder metallurgy templates for 3D graphene foams (PMT-GFs) consist of particle-like carbon shells which are connected by multilayered graphene that shows high specific surface area (1080 m(2) g(-1)), good crystallization, good electrical conductivity (13.8 S cm(-1)), and a mechanically robust structure. The PMT-GFs did not break under direct flushing with DI water, and they were able to recover after being compressed. These properties indicate promising applications of PMT-GFs for fields requiring 3D carbon frameworks such as in energy-based electrodes and mechanical dampening.

Laser‐Induced Graphene in Controlled Atmospheres: From Superhydrophilic to Superhydrophobic Surfaces

The modification of graphene-based materials is an important topic in the field of materials research. This study aims to expand the range of properties for laser-induced graphene (LIG), specifically to tune the hydrophobicity and hydrophilicity of the LIG surfaces. While LIG is normally prepared in the air, here, using selected gas atmospheres, a large change in the water contact angle on the as-prepared LIG surfaces has been observed, from 0° (superhydrophilic) when using O2 or air, to >150° (superhydrophobic) when using Ar or H2 . Characterization of the newly derived surfaces shows that the different wetting properties are due to the surface morphology and chemical composition of the LIG. Applications of the superhydrophobic LIG are shown in oil/water separation as well as anti-icing surfaces, while the versatility of the controlled atmosphere chamber fabrication method is demonstrated through the improved microsupercapacitor performance generated from LIG films prepared in an O2 atmosphere.

Three-Dimensional Printed Graphene Foams

An automated metal powder three-dimensional (3D) printing method for in situ synthesis of free-standing 3D graphene foams (GFs) was successfully modeled by manually placing a mixture of Ni and sucrose onto a platform and then using a commercial CO2 laser to convert the Ni/sucrose mixture into 3D GFs. The sucrose acted as the solid carbon source for graphene, and the sintered Ni metal acted as the catalyst and template for graphene growth. This simple and efficient method combines powder metallurgy templating with 3D printing techniques and enables direct in situ 3D printing of GFs with no high-temperature furnace or lengthy growth process required. The 3D printed GFs show high-porosity (∼99.3%), low-density (∼0.015g cm-3), high-quality, and multilayered graphene features. The GFs have an electrical conductivity of ∼8.7 S cm-1, a remarkable storage modulus of ∼11 kPa, and a high damping capacity of ∼0.06. These excellent physical properties of 3D printed GFs indicate potential applications in fields requiring rapid design and manufacturing of 3D carbon materials, for example, energy storage devices, damping materials, and sound absorption.

Laser-Induced Graphene Layers and Electrodes Prevents Microbial Fouling and Exerts Antimicrobial Action

Prevention of fouling on surfaces is a major challenge that broadly impacts society. Water treatment technologies, hospital infrastructure, and seawater pipes exemplify surfaces that are susceptible to biofouling. Here we show that laser-induced graphene (LIG) printed on a polyimide film by irradiation with a CO2 infrared laser under ambient conditions is extremely biofilm resistant while as an electrode is strongly antibacterial. We investigated the antibacterial activity of the LIG surface using LIG powder in suspension or deposited on surfaces, and its activity depended on the particle size and oxygen content. Remarkably, the antimicrobial effects of the surface were greatly amplified when voltages in the range of 1.1-2.5 were applied in an electrode configuration in bacterial solutions. The bactericidal mechanism was directly observed using microscopy and fast photography, which showed a rapid bacterial movement toward the LIG surface and subsequent bacterial killing. In addition, electrochemical generation of H2O2 was observed; however, the bacterial killing mechanism depended strongly on the physical and electrical contact of the bacterial cells to the surfaces. The anti-biofilm activity of the LIG surfaces and electrodes could lead to efficient protection of surfaces that are susceptible to biofouling in environmental applications by incorporating LIG onto the surfaces.