Nitrogen-Doped Carbon-Encased Bimetallic Selenide for High-Performance Water Electrolysis

Demand of highly efficient earth-abundant transition metal-based electrocatalysts to replace noble metal materials for boosting oxygen evolution reaction(OER)is rapidly growing.Herein,an electrochemically exfoliated graphite(EG)foil supported bimetallic selenide encased in N-doped carbon(EG/(Co,Ni)Se2-NC)hybrid is developed and synthesized by a vapor-phase hydrothermal strategy and subsequent selenization process.The as-prepared EG/(Co,Ni)Se2-NC hybrid exhibits a core-shell structure where the particle diameter of(Co,Ni)Se2 core is about 70 nm and the thickness of N-doped carbon shell is approximately 5 nm.Benefitting from the synergistic effects between the combination of highly active Co species and improved electron transfer from Ni species,and N-doped carbon,the EG/(Co,Ni)Se2-NC hybrid shows remarkable electrocatalytic activity toward OER with a comparatively low overpotential of 258 mV at an current density of 10 mA cm?2 and a small Tafel slope of 73.3 mV dec?1.The excellent OER catalysis performance of EG/(Co,Ni)Se2-NC hybrid is much better than that of commercial Ir/C(343 mV at 10 mA cm?2 and 98.1 mV dec?1),and even almost the best among all previously reported binary CoNi selenide-based OER electrocatalysts.Furthermore,in situ electrochemical Raman spectroscopy combined with ex situ X-ray photoelectron spectroscopy analysis indicates that the superb OER catalysis activity can be attributed to the highly active Co-OOH species and modified electron transfer process from Ni element.

Research on an innovative structure of an open-ribbed steel-ultra-high performance concrete composite bridge deck

To completely solve the problem of fatigue cracking issue of orthotropic steel bridge decks(OSDs),the authors proposed a steel–ultra-high performance concrete(UHPC)lightweight composite deck(LWCD)with closed ribs in 2010.Based on the successful application of that LWCD,an adaptation incorporating an innovative composite deck structure,i.e.,the hot-rolled section steel–UHPC composite deck with open ribs(SSD)is proposed in this paper,aiming to simplify the fabrication process as well as to reduce the cost of LWCD.Based on a long-span cable-stayed bridge,a design scheme is proposed and is compared with the conventional OSD scheme.Further,a finite element(FE)calculation is conducted to reflect both the global and local behavior of the SSD scheme,and it is found that the peaked stresses in the SSD components are less than the corresponding allowable values.A static test is performed for an SSD strip specimen to understand the anti-cracking behavior of the UHPC layer under negative bending moments.The static test results indicate that the UHPC layer exhibited a satisfactory tensile toughness,the UHPC tensile strength obtained from the test is 1.8 times the calculated stress by the FE model of the real bridge.In addition,the fatigue stresses of typical fatigue-prone details in the SSD are calculated and evaluated,and the influences of key design parameters on the fatigue performance of the SSD are analyzed.According to the fatigue results,the peaked stress ranges for all of the 10 fatigue-prone details are within the corresponding constant amplitude fatigue limits.Then a fatigue test is carried out for another SSD strip specimen to explore the fatigue behavior of the fillet weld between the longitudinal and transverse ribs.The specimen failed at the fillet weld after equivalent 47.5 million cycles of loading under the design fatigue stress range,indicating that the fatigue performance of the SSD could meet the fatigue design requirement.Theoretical calculations and experiments provide a basis for the promotion and application of this structure in bridge engineering.

Innovative steel-UHPC composite bridge girders for long-span bridges

Steel and steel-concrete composite girders are two types of girders commonly used for long-span bridges. However, practice has shown that the two types of girders have some drawbacks. For steel girders, the orthotropic steel deck (OSD) is vulnerable to fatigue cracking and the asphalt overlay is susceptible to damage such as rutting and pot holes. While for steel-concrete composite girders, the concrete deck is generally thick and heavy, and the deck is prone to cracking because of its low tensile strength and high creep. Thus, to improve the serviceability and durability of girders for long-span bridges, three new types of steel-UHPC lightweight composite bridge girders are proposed, where UHPC denotes ultra-high performance concrete. The first two types consist of an OSD and a thin UHPC layer while the third type consists of a steel beam and a UHPC waffle deck. Due to excellent mechanical behaviors and impressive durability of UHPC, the steel-UHPC composite girders have the advantages of light weight, high strength, low creep coefficient, low risk of cracking, and excellent durability, making them competitive alternatives for long-span bridges. To date, the proposed steel-UHPC composite girders have been applied to 14 real bridges in China. It is expected that the application of the new steel-UHPC composite girders on long-span bridges will have a promising future.