Modulating surface and interface chemistry for advancing electrochemical water splitting

Electrochemical water splitting is a promising alternative to produce hydrogen as a propitious energy carrier. It involves two half-reactions, hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). The large thermodynamic energy barrier and the sluggish kinetics of the multi-electron transfer OER necessitate developing highly efficient nonprecious metallic catalysts. Nickel (Ni) and iron (Fe) are earth-abundant and active metals for water splitting. However, the energy input to drive OER and HER is still large. Surface and interface chemistry modulation in Ni and Fe-based catalyst is a promising approach to increase the intrinsic activity and catalytic efficiency. Such a strategy requires steps to regulate the electronic properties of surface active sites and accelerate the evolution dynamics of gas bubble products. Here, surface modification of Ni and Fe-based catalysts via several oxide functional groups including borate (BO3), vanadate (VO4), and molybdate (MoO4) is demonstrated as a practical approach to reduce the energy barrier required to initiate OER as well as its electrocatalysis at large currents. Both the electronic properties of surface active sites and surface wettability are enhanced when modified with these functional groups. Also, Vanadate and molybdate oxo-anions are observed to regulate the intermetallic synergy to augment the intrinsic activity. Such synergistic effect promoted by surface oxo-anionic modification induces in situ phase transformation in FeNi vanadate and molybdate catalysts. Furthermore, this strategy endows superhydrophilic surfaces to Fe and FeNi catalysts which accelerates the gas bubble growth and dissipation. In addition, surface nano- structuring is another approach to promote electrocatalytic performance. A bio-inspired hetero- hierarchical nanostructure based on Ni is developed for HER, which involves nano-hetero- interfaces between Ni(OH)2 and NiNx-C microenvironments. Such nano-hetero-interfacing accelerates HER kinetics via an interphasic synergy between Ni(OH)2 and NiNx-C phases. Surface hierarchies achieved by nano-structuring are effective for gas bubble evolution dynamics, resulting in ultra-large current densities at low energy input. The results in this thesis demonstrate new insights for concepts including intermetallic and interphasic synergy and gas bubble evolution, which are effective in developing highly efficient non-precious metal-based catalysts for water splitting

Noble-Metal-Free Multicomponent Nanointegration for Sustainable Energy Conversion

Global energy and environmental crises are among the most pressing challenges facing humankind. To overcome these challenges, recent years have seen an upsurge of interest in the development and production of renewable chemical fuels as alternatives to the nonrenewable and high-polluting fossil fuels. Photocatalysis, photoelectrocatalysis, and electrocatalysis provide promising avenues for sustainable energy conversion. Single- and dual-component catalytic systems based on nanomaterials have been intensively studied for decades, but their intrinsic weaknesses hamper their practical applications. Multicomponent nanomaterial-based systems, consisting of three or more components with at least one component in the nanoscale, have recently emerged. The multiple components are integrated together to create synergistic effects and hence overcome the limitation for outperformance. Such higher-efficiency systems based on nanomaterials will potentially bring an additional benefit in balance-of-system costs if they exclude the use of noble metals, considering the expense and sustainability. It is therefore timely to review the research in this field, providing guidance in the development of noble-metal-free multicomponent nanointegration for sustainable energy conversion. In this work, we first recall the fundamentals of catalysis by nanomaterials, multicomponent nanointegration, and reactor configuration for water splitting, CO2 reduction, and N2 reduction. We then systematically review and discuss recent advances in multicomponent-based photocatalytic, photoelectrochemical, and electrochemical systems based on nanomaterials. On the basis of these systems, we further laterally evaluate different multicomponent integration strategies and highlight their impacts on catalytic activity, performance stability, and product selectivity. Finally, we provide conclusions and future prospects for multicomponent nanointegration. This work offers comprehensive insights into the development of cost-competitive multicomponent nanomaterial-based systems for sustainable energy-conversion technologies and assists researchers working toward addressing the global challenges in energy and the environment.Haijiao Lu, Julie Tournet, Kamran Dastafkan, Yun Liu, Yun Hau Ng, Siva Krishna Karuturi, Chuan Zhao, and Zongyou Yi

Recent advances in spinel-type electrocatalysts for bifunctional oxygen reduction and oxygen evolution reactions

Abstract not available.Xiao-Meng Liu , Xiaoyang Cui , Kamran Dastafkan , Hao-Fan Wang , Cheng Tang, Chuan Zhao , Aibing Chen , Chuanxin He , Minghan Han , Qiang Zhan