Mark James Biggs

There is great interest in systems where enzymes are adsorbed on and act at electrode surfaces – enzymatic biofuel cells, bioreactors and biosensors are just three examples. Whilst such systems have been the subject of extensive study and development since the 1960s, the rate of progress in this research is hindered by a lack of molecular-level understanding of the enzyme adsorption process and adsorbed states, and the associated electron transfer processes. Herein, we present and then demonstrate a multiscale approach that combines molecular dynamics simulation to elucidate the former and density functional theory (MD/DFT) for the latter. The demonstration of the new approach focused on a system involving the microperoxidase-11 (MP-11) enzyme, a microenzyme made up of a Fe-containing heme ring attached to an 11-residue scaffold, a graphene electrode, and a neutral-pH saline solution. For this system, the adsorbed MP-11 was found to adopt six possible heme configurations, where the configurations are defined by the distance of the iron from the graphene and the angle between the normals of the heme ring and graphene electrode. The rate constant for electron transfer between the MP-11 and graphene evaluated through combining the MD and DFT results and their variation with overpotential are comparable to the limited experimental data. The results were used to illustrate how the new multiscale approach could be used to improve electrocatalytic performance of the system.

Constructing {110}‐textured lithium (Li) metal anodes is a promising strategy to extend battery life. While preparation of such anodes has been the subject of a few studies, their focus has been exclusively on thermodynamically‐driven (equilibrium) strategies. Through a systematic screening of bath conditions, the study reported here identifies a novel kinetically‐driven protocol that enhances the volume fraction of {110} texture by more than fivefold compared to equilibrium approaches. The protocol involves Li deposition at high current densities or low temperatures in a commonly used LiNO₃‐containing ether‐based electrolyte. Columnar {110}‐oriented grains are formed through a growth rate selection process arising from the stronger electronic coupling and faster electron transfer rate between Li(110) and Li⁺ cations compared to other lattice planes. LiNO₃ plays a crucial role by inhibiting the deposition on the Li(110) plane less than the other planes. Simple bath condition adjustments yield optimized {110}‐textured Li anodes with improved plating/stripping homogeneity that suppresses dendrite formation and electrolyte consumption, resulting in extended cycle life in lean‐electrolyte full cells. This kinetically‐driven approach offers mechanistic insight into Li texture formation and a promising route to high‐performance Li metal anodes.

An efficient Li–S redox catalyst consisting of MWCNTs covalently modified by cobalt(II) tetraaminophthalocyanines (TaPcCo‐MWCNTs) is developed. Effective lithium polysulfide (LiPS) capturing is enabled by the lithiophilic N‐containing phthalocyanine rings and the sulfiphilic Co central atoms. This adsorption geometry utilizes the Co unoccupied d‐orbitals as electron super‐exchange highways. Elevated kinetics of LiPSs reactions in the liquid phase as well as liquid–solid transitions were revealed by electrochemical measurements and density functional theory calculations. Uniform deposition of Li₂S films was also observed, which preserves cathode integrity and sulfur utilization during cell cycling. The catalyzed sulfur redox is also significantly facilitated by the fast electron and Li‐ion transport to and from the reaction sites through the conductive MWCNT skeletons and the lithiophilic substituent amino groups on TaPcCo. With 6 wt % addition of TaPcCo‐MWCNT in the cathode coatings, high sulfur utilization is achieved with areal sulfur loadings of up to 7 mg cm⁻². Stable long‐term cycling is achieved at 1 C at a sulfur loading of 5 mg cm⁻², with an initial areal capacity of 4.4 mAh cm⁻² retention of 3.5 mAh cm⁻² after 500 cycles. Considering the high structural diversity of phthalocyanines macromolecules, this study provides opportunities for a new class of Li–S catalysts.

Peptide adsorption occurs across technology, medicine, and nature. The functions of adsorbed peptides are related to their conformation. In the past, molecular simulation methods such as molecular dynamics have been used to determine key conformations of adsorbed peptides. However, the transitions between these conformations often occur too slowly to be modeled reliably by such methods. This means such transitions are less well understood. In the study reported here, discrete path sampling is used for the first time to study the potential energy surface of an adsorbed peptide (polyalanine) and the transition pathways between various stable adsorbed conformations that have been identified in prior work by two of the authors [ Mijajlovic , M. ; Biggs , M. J. J. Phys. Chem. C 2007 , 111 , 15839−15847]. Mechanisms for the switching of adsorbed polyalanine between the stable conformations are elucidated along with the energetics of these switches.

Free-standing high performance Li–S battery cathodes are currently attracting significant research efforts. Loose macroporous structures have been proposed by many to improve sulfur utilization and areal capacity. However, their low cathode sulfur densities and high electrolyte fractions lead to low cell volumetric and gravimetric capacities. We report here a compact free-standing Li–S cathode structure that delivers areal, volumetric and gravimetric capacities all exceeding those of typical Li-ion batteries. The cathodes, formed by pressure filtration of the constituents, are composed of highly micro/mesoporous nitrogen-doped carbon nanospheres (NCNSs) embedded in the macropores of a multi-walled carbon nanotube (MWCNT) network to form a dense structure. The MWCNT network facilitates low cathode impedance. The NCNSs maximize sulfur utilization and immobilization. These collectively result in high cathode volumetric capacity (1106 mA h cm⁻³) and low electrolyte requirement (6 μL mg⁻¹ of sulfur), which together lead to high cell-level gravimetric capacity. Stable long-term cycling at 0.3C (2.5 mA cm⁻² for 5 mg cm⁻² areal sulfur-loading) has also been achieved, with the areal and volumetric capacities of the best remaining above typical Li-ion values over 270 cycles and the per-cycle capacity fading being only 0.1%. The facile preparation means significant potential for large scale use.

This study reports a Li–S battery cathode of high volumetric capacity enabled by novel micro‐ and mesostructuring. The cathode is based on monodisperse highly porous carbon nanospheres derived from a facile template‐ and surfactant‐free method. At the mesoscale, the nanospheres structure into interconnected close‐packed clusters of a few microns in extent, thus facilitating the fabrication of dense crack‐free high areal sulfur loading (5 mg cm⁻²) cathodes with high electrical conductivity and low cathode impedance. A combination of the nitrogen doping (5 wt%), high porosity (2.3 cm³ g⁻¹), and surface area (2900 m² g⁻¹) at the microscale enables high sulfur immobilization and utilization. The cathode delivers among the best reported volumetric capacity to date, above typical Li‐ion areal capacity at 0.2 C over 200 cycles and low capacity fading of 0.1% per cycle at 0.5 C over 500 cycles. The compact cathode structure also ensures a low electrolyte requirement (6 µL mg⁻¹), which aids a low overall cell weight, and further, among the best gravimetric capacities published to date as well.