Engineering topics

Sun, Cheng-Jun

Publications and source records attributed to Sun, Cheng-Jun.

58 records · Page 4

DOE OSTI2020

Durable hybrid electrocatalysts for proton exchange membrane fuel cells

The low durability of carbon-based non-precious metal electrocatalysts hinders their practical applications in proton exchange membrane fuel cells (PEMFCs). In this study, we rationally design a hybrid Pt-Fe-N-C electrocatalyst with unprecedented durability. It consists of abundant Pt and Fe single atoms homogeneously dispersed on the nitrogen-doped carbon support and a small amount of Pt-Fe alloy nanoparticles. A PEMFC with Pt-Fe-N-C as the cathode shows a larger peak power density (0.75 W cm -2 ) than that with Fe-N-C as the cathode (0.50 W cm -2 ). The remarkable durability of Pt-Fe-N-C is reflected from no noticeable drop in the half-wave potential after 70000 potential cycles between 0.6 and 1.0 V in the liquid cell, and 80% current retention after 85 h of potential hold at 0.4 V in the fuel cell. This work demonstrates the feasibility of improving the durability of Fe-N-C material via ultra-low Pt doping and makes non-precious metal electrocatalysts be close to achieving commercial metrics.

25 ENERGY STORAGE↗

DOE OSTI2020

Highly Reversible Sodiation/Desodiation from a Carbon-Sandwiched SnS2 Nanosheet Anode for Sodium Ion Batteries

The further improvement of sodium ion batteries requires the elucidation of the mechanisms pertaining to reversibility, which allows the novel design of the electrode structure. Her; through a hydrogel-embedding method, we are able to confine the growth of few-layer SnS 2 nanosheets between a nitrogen- and sulfur-doped carbon nanotube (NS-CNT) and amorphous carbon. The obtained carbon-sandwiched SnS 2 nanosheets demonstrate excellent sodium storage properties. In operando small-angle X-ray scattering combined with the ex situ X-ray absorption near edge spectra reveal that the redox reactions between SnS 2 /NS-CNT and the sodium ion are highly reversible. Furthermore, on the contrary, the nanostructure evolution is found to be irreversible, in which the SnS 2 nanosheets collapse, followed by the regeneration of SnS 2 nanoparticles. This work provides operando insights into the chemical environment evolution and structure change of SnS 2 -based anodes, elucidating its reversible reaction mechanism, and illustrates the significance of engineered carbon support in ensuring the electrode structure stability.

25 ENERGY STORAGE↗

DOE OSTI2020

Structural and Electrochemical Impacts of Mg/Mn Dual Dopants on the LiNiO 2 Cathode in Li-Metal Batteries

Doping chemistry has been regarded as an efficient strategy to overcome some fundamental challenges facing the “no-cobalt” LiNiO 2 cathode materials. By utilizing the doping chemistry, we evaluate the battery performance and structural/chemical reversibility of a new no-cobalt cathode material (Mg/Mn-LiNiO 2 ). The unique dual dopants drive Mg and Mn to occupy the Li site and Ni site, respectively. We report the Mg/Mn-LiNiO 2 cathode delivers smooth voltage profiles, enhanced structural stability, elevated self-discharge resistance, and inhibited nickel dissolution. As a result, the Mg/Mn-LiNiO 2 cathode enables improved cycling stability in lithium metal batteries with the conventional carbonate electrolyte: 80% capacity retention after 350 cycles at C /3, and 67% capacity retention after 500 cycles at 2 C (22 °C). We then take the Mg/Mn-LiNiO 2 as the platform to investigate the local structural and chemical reversibility, where we identify that the irreversibility takes place starting from the very first cycle. The highly reactive surface induces the surface oxygen loss, metal reduction reaching the subsurface, and metal dissolution. Our data demonstrate that the dual dopants can, to some degree, mitigate the irreversibility and improve the cycling stability of LiNiO 2 , but more efforts are needed to eliminate the key challenges of these materials for battery operation in the conventional carbonate electrolyte.

25 ENERGY STORAGE↗

DOE OSTI2020

Broadband Tunable Mid-infrared Plasmon Resonances in Cadmium Oxide Nanocrystals Induced by Size-Dependent Nonstoichiometry

A central theme of nanocrystal (NC) research involves synthesis of dimension-controlled NCs and study of size-dependent scaling laws governing their optical, electrical, magnetic, and thermodynamic properties. In this paper, we describe the synthesis of monodisperse CdO NCs that exhibit high quality-factor (up to 5.5) mid-infrared (MIR) localized surface plasmon resonances (LSPR) and elucidate the inverse scaling relationship between carrier concentration and NC size. The LSPR wavelength is readily tunable between 2.4 and similar to 6.0 μm by controlling the size of CdO NCs. Structural and spectroscopic characterization provide strong evidence that free electrons primarily originate from self-doping due to NC surface-induced nonstoichiometry. The ability to probe and to control NC stoichiometry and intrinsic defects will pave the way toward predictive synthesis of doped NCs with desirable LSPR characteristics.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗