Engineering topics

Xia, Chuan

Publications and source records attributed to Xia, Chuan.

4 records

DOE OSTI2021

General synthesis of single-atom catalysts with high metal loading using graphene quantum dots

Transition-metal single-atom catalysts present extraordinary activity per metal atomic site, but suffer from low metal-atom densities (typically less than 5 wt% or 1 at.%), which limits their overall catalytic performance. Here we report a general method for the synthesis of single-atom catalysts with high transition-metal-atom loadings of up to 40 wt% or 3.8 at.%, representing several-fold improvements compared to benchmarks in the literature. Graphene quantum dots, later interweaved into a carbon matrix, were used as a support, providing numerous anchoring sites and thus facilitating the generation of high densities of transition-metal atoms with sufficient spacing between the metal atoms to avoid aggregation. A significant increase in activity in electrochemical CO 2 reduction (used as a representative reaction) was demonstrated on a Ni single-atom catalyst with increased Ni loading.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2021

Electrochemical ammonia synthesis via nitrate reduction on Fe single atom catalyst

Electrochemically converting nitrate, a widespread water pollutant, back to valuable ammonia is a green and delocalized route for ammonia synthesis, and can be an appealing and supplementary alternative to the Haber-Bosch process. However, as there are other nitrate reduction pathways present, selectively guiding the reaction pathway towards ammonia is currently challenged by the lack of efficient catalysts. Here we report a selective and active nitrate reduction to ammonia on Fe single atom catalyst, with a maximal ammonia Faradaic efficiency of ~ 75% and a yield rate of up to ~ 20,000 μg h –1 mg cat. –1 (0.46 mmol h –1 cm –2 ). Our Fe single atom catalyst can effectively prevent the N-N coupling step required for N 2 due to the lack of neighboring metal sites, promoting ammonia product selectivity. Density functional theory calculations reveal the reaction mechanisms and the potential limiting steps for nitrate reduction on atomically dispersed Fe sites.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2019

Artificial Solid Electrolyte Interphase for Suppressing Surface Reactions and Cathode Dissolution in Aqueous Zinc Ion Batteries

Vanadium-based compounds have been widely used as electrode materials in aqueous zinc ion batteries (ZIBs) due to the multiple oxidation states of vanadium and their open framework structure. However, the solubility of vanadium in aqueous electrolytes and the formation of byproducts during the charge/discharge process cause severe capacity fading and limit cycle life. Here in this paper, we report an ultrathin HfO 2 film as an artificial solid electrolyte interphase (SEI) that is uniformly and conformally deposited by atomic layer deposition (ALD). The inactive hafnium(IV) oxide (HfO 2 ) film not only decreases byproduct (Zn 4 SO 4 (OH) 6 ·xH 2 O) formation on the surface of Zn 3 V 2 O 7 (OH) 2 ·2H 2 O (ZVO) but also suppresses the ZVO cathode dissolution in the electrolyte. As a result, the obtained HfO 2 -coated ZVO cathodes deliver higher capacity and better cycle life (227 mAh g –1 @100 mA g –1 , 90% retention over 100 cycles) compared with pristine ZVO (170 mAh g –1 @100 mA g –1 , 45% retention over 100 cycles). A mechanistic investigation of the role of HfO 2 is presented, along with data showing that our method constitutes a general strategy for other cathodes to enhance their performance in aqueous ZIBs.

25 ENERGY STORAGE↗

DOE OSTI2019

Continuous production of pure liquid fuel solutions via electrocatalytic CO 2 reduction using solid-electrolyte devices

Electrocatalytic CO 2 reduction is often carried out in a solution electrolyte such as KHCO 3 (aq), which allows for ion conduction between electrodes. Thus, liquid products that form are in a mixture with the dissolved salts, requiring energy-intensive downstream separation. In this work, we report continuous electrocatalytic conversion of CO 2 to pure liquid fuel solutions in cells that utilize solid electrolytes, where electrochemically generated cations (such as H+) and anions (such as HCOO–) are combined to form pure product solutions without mixing with other ions. Using a HCOOH-selective (Faradaic efficiencies>90%) and easily scaled Bi catalyst at the cathode, we demonstrate production of pure HCOOH solutions with concentrations up to 12M. We also show 100h continuous and stable generation of 0.1 M HCOOH with negligible degradation in selectivity and activity. Production of other electrolyte-free C 2+ liquid oxygenate solutions, including acetic acid, ethanol and n-propanol, are also demonstrated using a Cu catalyst. Lastly, we show that our CO 2 reduction cell with solid electrolytes can be modified to suit other, more complex practical applications.

36 MATERIALS SCIENCE↗