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- Lithium–copper alloy embedded in 3D porous copper foam with enhanced electrochemical performance toward lithium metal batteriesPublication . Lu, Ziyu; Tai, Zhixin; Yu, Zhipeng; LaGrow, Alec P.; Bondarchuk, Oleksandr; Sousa, Juliana P.S.; Meng, Lijian; Peng, Zhijian; Liu, LifengSuppressing dendrite growth and accommodating volume change, among others, are the main challenges for lithium (Li) metal anode to be used in rechargeable Li batteries. The commercial macroporous copper (Cu) foam current collector may only tackle these challenges to a little extent, and it is usually unable to provide sufficient Li nucleation sites, leading to rapidly increased polarization and unstable cycling performance. Herein, we report a three-dimensional composite anode comprising Li–Cu alloy melt-cast on a commercial Cu foam (CF) current collector (Li–Cu/CF), which can be converted to a unique architecture consisting of Li metal supported by an interconnected CuLix alloy nanowire network formed because of the phase separation, when the molten Li–Cu alloy cools down and gets solidified. Compared to the bare Li foil, the Li–Cu/CF anode shows a smaller polarization and better cycle stability in the carbonate electrolyte at various current densities ranging from 1 to 5 mA/cm2 and is free from dendrite growth upon repeated Li plating/stripping. This can be attributed to the low Li nucleation overpotential and high Coulombic efficiency (96%) during Li plating on and stripping from the thus-obtained hierarchically structured CF collector, as well as the higher proportion of Li2O relative to LiF in the solid-electrolyte interphase layer. Moreover, when assembled in a full cell paired with the LiFePO4 cathode, the Li–Cu/CF anode also exhibits much better rate capability and cycle performance than the bare Li foil. Our work provides a new convenient approach to construct a dendrite-free Li metal anode that can be potentially deployed in the next-generation high energy density rechargeable Li batteries.
- Iridium–Iron Diatomic Active Sites for Efficient Bifunctional Oxygen ElectrocatalysisPublication . Yu, Zhipeng; Si, Chaowei; LaGrow, Alec P.; Tai, Zhixin; Caliebe, Wolfgang A.; Tayal, Akhil; Sampaio, Maria J.; Sousa, Juliana P. S.; Amorim, Isilda; Araujo, Ana; Meng, Lijian; Faria, Joaquim L.; Xu, Junyuan; Li, Bo; Liu, LifengDiatomic catalysts, particularly those with heteronuclear active sites, have recently attracted considerable attention for their advantages over single-atom catalysts in reactions involving multielectron transfers. Herein, we report bimetallic iridium−iron diatomic catalysts (IrFe−N−C) derived from metal−organic frameworks in a facile wet chemical synthesis followed by postpyrolysis. We use various advanced characterization techniques to comprehensively confirm the atomic dispersion of Ir and Fe on the nitrogen-doped carbon support and the presence of atomic pairs. The asobtained IrFe−N−C shows substantially higher electrocatalytic performance for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) when compared to the single-atom counterparts (i.e., Ir−N−C and Fe−N−C), revealing favorable bifunctionality. Consequently, IrFe−N−C is used as an air cathode in zinc− air batteries, which display much better performance than the batteries containing commercial Pt/C + RuO2 benchmark catalysts. Our synchrotron-based X-ray absorption spectroscopy experiments and density functional theory (DFT) calculations suggest that the IrFe dual atoms presumably exist in an IrFeN6 configuration where both Ir and Fe coordinates with four N atoms and two N atoms are shared by the IrN4 and FeN4 moieties. Furthermore, the Fe site contributes mainly to the ORR, while the Ir site plays a more important role in the OER. The dual-atom sites work synergistically, reducing the energy barrier of the rate-determining step and eventually boosting the reversible oxygen electrocatalysis. The IrFe−N−C catalysts hold great potential for use in various electrochemical energy storage and conversion devices.
- Novel Quasi‐Liquid K‐Na Alloy as a Promising Dendrite‐Free Anode for Rechargeable Potassium Metal BatteriesPublication . Tai, Zhixin; Li, Yi; Liu, Yajie; Zhao, Lanling; Ding, Yu; Lu, Ziyu; Peng, Zhijian; Meng, Lijian; Yu, Guihua; Liu, LifengRechargeable potassium metal batteries are promising energy storage devices with potentially high energy density and markedly low cost. However, eliminating dendrite growth and achieving a stable electrode/electrolyte interface are the key challenges to tackle. Herein, a novel "quasi-liquid" potassium-sodium alloy (KNA) anode comprising only 3.5 wt% sodium (KNA-3.5) is reported, which exhibits outstanding electrochemical performance able to be reversibly cycled at 4 mA cm-2 for 2000 h. Moreover, it is demonstrated that adding a small amount of sodium hexafluorophosphate (NaPF6 ) into the potassium bis(fluorosulfonyl)imide electrolyte allows for the formation of the "quasi-liquid" KNA on electrode surface. Comprehensive experimental studies reveal the formation of an unusual metastable KNa2 phase during plating, which is believed to facilitate simultaneous nucleation and suppress the growth of dendrites, thereby improving the electrode's cycle lifetime. The "quasi-liquid" KNA-3.5 anode demonstrates markedly enhanced electrochemical performance in a full cell when pairing with Prussian blue analogs or sodium rhodizonate dibasic as the cathode material, compared to the pristine potassium anode. Importantly, unlike the liquid KNA reported before, the "quasi-liquid" KNA-3.5 exhibits good processability and can be readily shaped into sheet electrodes, showing substantial promise as a dendrite-free anode in rechargeable potassium metal batteries.
- Defective Ru-doped α-MnO2 nanorods enabling efficient hydrazine oxidation for energy-saving hydrogen production via proton exchange membranes at near-neutral pHPublication . Yu, Zhipeng; Si, Chaowei; Sabaté, Ferran; LaGrow, Alec P.; Tai, Zhixin; Diaconescu, Vlad Martin; Simonelli, Laura; Meng, Lijian; Sabater, Maria J.; Li, Bo; Liu, LifengProton exchange membrane water electrolysis (PEMWE) showes substantial advantages over the conventional alkaline water electrolysis (AWE) for power-to-hydrogen (PtH) conversion, given the faster response and wider dynamic current range of the PEMWE technology. However, PEMWE is currently still expensive due partly to the high voltage needed to operate at high current densities and inevitable usage of precious iridium/rutheniumbased catalysts to expedite the slow kinetics of the oxygen evolution reaction (OER) and to ensure sufficient durability under strongly acidic conditions. Herein, we report that ruthenium doped α-manganese oxide (Ru/ α-MnO2) nanorods show outstanding electrocatalytic performance toward the hydrazine (N2H4) oxidation reaction (HzOR) in near-neutral media (weak alkaline and weak acid), which can be used to replace the energydemanding OER for PEMWE. The as-prepared Ru/α-MnO2 is found to comprise abundant defects. When used to catalyze HzOR in the acid-hydrazine electrolyte (0.05 M H2SO4 + 0.5 M N2H4), it can deliver an anodic current density of 10 mA cm 2 at a potential as low as 0.166 V vs. reversible hydrogen electrode (RHE). Moreover, Ru/ α-MnO2 exhibits remarkable corrosion/oxidation resistance and remains electrochemically stable during HzOR for at least 1000 h. Theoretical calculations and experimental studies prove that Ru doping elongates the Mn–O bond and produces abundant cationic defects, which induces charge delocalization and significantly lowers material’s electrical resistance and overpotential, resulting in excellent HzOR catalytic activity and stability. The introduction of N2H4 significantly reduces the energy demand for hydrogen production, so that PEMWE can be accomplished under remarkably low voltages of 0.254 V at 10 mA cm 2 and 0.935 V at 100 mA cm 2 for a long term without notable degradation. This work opens a new avenue toward energy-saving PEMWE with earthabundant OER catalysts.
- Novel Quasi‐Liquid K‐Na Alloy as a Promising Dendrite‐Free Anode for Rechargeable Potassium Metal BatteriesPublication . Tai, Zhixin; Li, Yi; Liu, Yajie; Zhao, Lanling; Ding, Yu; Lu, Ziyu; Peng, Zhijian; Meng, Lijian; Yu, Guihua; Liu, LifengRechargeable potassium metal batteries are promising energy storage devices with potentially high energy density and markedly low cost. However, eliminating dendrite growth and achieving a stable electrode/electrolyte interface are the key challenges to tackle. Herein, a novel “quasi-liquid” potassium-sodium alloy (KNA) anode comprising only 3.5 wt% sodium (KNA-3.5) is reported, which exhibits outstanding electrochemical performance able to be reversibly cycled at 4 mA cm–2 for 2000 h. Moreover, it is demonstrated that adding a small amount of sodium hexafluorophosphate (NaPF6) into the potassium bis(fluorosulfonyl)imide electrolyte allows for the formation of the “quasi-liquid” KNA on electrode surface. Comprehensive experimental studies reveal the formation of an unusual metastable KNa2 phase during plating, which is believed to facilitate simultaneous nucleation and suppress the growth of dendrites, thereby improving the electrode's cycle lifetime. The “quasi-liquid” KNA-3.5 anode demonstrates markedly enhanced electrochemical performance in a full cell when pairing with Prussian blue analogs or sodium rhodizonate dibasic as the cathode material, compared to the pristine potassium anode. Importantly, unlike the liquid KNA reported before, the “quasi-liquid” KNA-3.5 exhibits good processability and can be readily shaped into sheet electrodes, showing substantial promise as a dendrite-free anode in rechargeable potassium metal batteries.
- Defective Ru-doped α-MnO2 nanorods enabling efficient hydrazine oxidation for energy-saving hydrogen production via proton exchange membranes at near-neutral pHPublication . Yu, Zhipeng; Si, Chaowei; Sabaté, Ferran; LaGrow, Alec P.; Tai, Zhixin; Diaconescu, Vlad Martin; Simonelli, Laura; Meng, Lijian; Sabater, Maria J.; Li, Bo; Liu, LifengProton exchange membrane water electrolysis (PEMWE) showes substantial advantages over the conventional alkaline water electrolysis (AWE) for power-to-hydrogen (PtH) conversion, given the faster response and wider dynamic current range of the PEMWE technology. However, PEMWE is currently still expensive due partly to the high voltage needed to operate at high current densities and inevitable usage of precious iridium/ruthenium-based catalysts to expedite the slow kinetics of the oxygen evolution reaction (OER) and to ensure sufficient durability under strongly acidic conditions. Herein, we report that ruthenium doped α-manganese oxide (Ru/α-MnO2) nanorods show outstanding electrocatalytic performance toward the hydrazine (N2H4) oxidation reaction (HzOR) in near-neutral media (weak alkaline and weak acid), which can be used to replace the energy-demanding OER for PEMWE. The as-prepared Ru/α-MnO2 is found to comprise abundant defects. When used to catalyze HzOR in the acid-hydrazine electrolyte (0.05 M H2SO4 + 0.5 M N2H4), it can deliver an anodic current density of 10 mA cm−2 at a potential as low as 0.166 V vs. reversible hydrogen electrode (RHE). Moreover, Ru/α-MnO2 exhibits remarkable corrosion/oxidation resistance and remains electrochemically stable during HzOR for at least 1000 h. Theoretical calculations and experimental studies prove that Ru doping elongates the Mn–O bond and produces abundant cationic defects, which induces charge delocalization and significantly lowers material’s electrical resistance and overpotential, resulting in excellent HzOR catalytic activity and stability. The introduction of N2H4 significantly reduces the energy demand for hydrogen production, so that PEMWE can be accomplished under remarkably low voltages of 0.254 V at 10 mA cm−2 and 0.935 V at 100 mA cm−2 for a long term without notable degradation. This work opens a new avenue toward energy-saving PEMWE with earth-abundant OER catalysts.