In Situ Creation of Surface Defects on Pd@NiPd with Core-shell Hierarchical Structure Toward Boosting Electrocatalytic Activity.

A deep insight into surface structural evolution of the catalyst is a challenging issue to reveal the structure-activity relationship. In this contribution, based on a surface alloying strategy, the dual-functional Pd@NiPd catalyst with a unique core-shell hierarchical structure is developed through selective crystal growth, surface cocrystallization, directional self-assembly, and reduction process. The surface defects are created in situ on the outer NiPd alloy layer in the electrochemical redox processes, which endow the Pd@NiPd catalyst with excellent electrocatalytic activity of hydrogen generation reaction (HER) and oxygen generation reaction (OER) in alkaline media. The optimal Pd@NiPd-2 catalyst requires an overpotential of only 18 mV that is far lower than Pt/C benchmark (43 mV) at the current density of 10 mA cm-2 for the HER, and 210 mV that is far lower than RuO2 benchmark (430 mV) at 50 mA cm-2 for the OER. Density functional theory (DFT) calculations reveal that the outstanding electrocatalytic activity is originated from the creation of surface defect structure that induces a significant reduction in the adsorption and dissociation energy barriers of H2O molecules in the HER and a decrease in the conversion energy from O* to OOH* that resulted from the synergy of two adjacent Pd sites by forming O-bridge. This work affords a typical paradigm for exploiting efficient catalysts and investigating the dependence of electrocatalytic activity on the surface structural evolution.

Nitrogen-doped biomass carbon fibers with surface encapsulated Co nanoparticles for electrocatalytic overall water-splitting.

N-Doped biomass carbon fibers with surface encapsulated Co nanoparticles (Co/N-BCFs) are prepared by the in situ structure-directing effect of the Co-complex formed with 2,2-bipyridine. An electrolyzer equipped with a Co/N-BCFs electrode couple only needs a voltage of 1.31 V at 10 mA cm-2 for overall water-splitting, which is better than that of an integrated RuO2 and Pt/C couple.

Nickel supported on Nitrogen-doped biomass carbon fiber fabricated via in-situ template technology for pH-universal electrocatalytic hydrogen evolution.

Developing alternatives to noble metal electrocatalysts for hydrogen production via water splitting is a challenging task. Herein, a novel electrocatalyst with Ni nanoparticles disperesed on N-doped biomass carbon fibers (NBCFs) was prepared through a simple in-situ growth process using Ni-ethanediamine complex (NiC) as the structure-directing agent. The in-situ template effect of the NiC facilitated the formation of Ni-N bonds between the Ni nanoparticles and NBCFs, which not only prevented the aggregation and corrosion of the Ni nanoparticles, but also accelerated the electron transfer in the electrochemical reaction, thus improving the hydrogen evolution reaction (HER) activity of the electrocatalyst. As expected, the optimal Ni/NBCF-1-H2 electrocatalyst exhibited better HER activity over the entire pH range than the control Ni/NBCF-1-N2 and Ni/NBCF-1-NaBH4 samples. The HER overpotentials of the Ni/NBCF-1-H2 electrocatalyst were as low as 47, 56, and 100 mV in alkaline (pH = 13.8), acidic (pH = 0.3), and neutral (pH = 7.3) electrolytes, respectively at the current density of 10 mA cm-2. Meanwhile, the Ni/NBCF-1-H2 sample could run continuously for 100 h, exhibiting outstanding stability. This work provides a feasible method for developing efficient and cheap electrocatalysts derived from biomass carbon materials using the in-situ template technology.

Fabrication of Co(Ni)-P surface bonding states on core-shell Co(OH)2@P-NiCo-LDH towards electrocatalytic hydrogen evolution reaction.

The application of NiCo-LDHs in the hydrogen evolution reaction (HER) is rarely reported because it is usually served as an effective electrocatalyst for oxygen evolution reaction (OER) owing to the essential chemical and electric structure features. It still is a challenge to realize the effective HER over NiCo-LDHs unless modified with noble metals. In this work, the noble-metal-free core-shell Co(OH)2@P-NiCo-LDH hybrid with dodecahedral hierarchical structure is prepared by the sacrificial template method along with subsequent phosphating process, which is available for the electrocatalytic HER. The fabricated Co(Ni)δ+-Pδ- bonding states on the surface of outer shell NiCo-LDH not only provide the abundant active centers but also reduce interfacial charge transfer resistance to enhance the HER activity. Meanwhile, the unique core-shell dodecahedral structure effectively avoids the agglomeration and restacking of NiCo-LDH nanosheets to improve the electrochemical stability. This work exploits a novel noble-metal-free modification strategy to expand the application of NiCo-LDH in HER.