Understanding and Optimizing Ultra‐Thin Coordination Polymer Derivatives with High Oxygen Evolution Performance

Abstract

fuel shortage and climate change. [1] Noble metal-based materials (e.g., Pt and its alloys) have been well investigated and are among the most promising electrocatalysts for water splitting to generate clean hydrogen. [2,3] However, Pt group-based catalysts are still constrained by their scarcity and high cost for scalable and commercial electrocatalysis. Hence, the development of noble-metal-free catalysts with comparable catalytic activity and robust durability is an urgent task to realize technical applications of water electrolysis. [4,5] Coordination polymer assemblies (CPAs), which are composed of a metal center linked to organic or inorganic ligands combine tunable porous structures, well-dispersed metal sites, high surface areas, and good chemical stability. This renders them excellent materials for drug delivery, [6] gas storage and separation, [7] batteries, [8,9] and catalysis. [10-13] Thanks to their unique structural properties, transition metal-based CPAs keep attracting broad interest in the field of heterogeneous electrocatalysts. [9a,b-14] However, their intrinsic poor conductivity, low mass permeability, and confined active metal centers need to be systematically improved for their application as efficient electrocatalysts. Moreover, instability issues of the ligands such as self-oxidation or degradation at high oxidation potentials need to be resolved for directly using CPAs as long-term electrocatalysts. [14-17] Several strategies, for example, morphological modulation, electronic tuning, and surface modification, have been confirmed as promising approaches to improve the electrocatalytic performance of CPAs and CPs. [14,16-21] In a representative study, ultra-thin NiCo bimetallic CPA nanosheets with enhanced OER activity compared to bulk NiCo bimetallic CPAs, were synthesized through an ultrasonication exfoliation method. [14] Zhang et al. [16] demonstrated that monolayered heterogenous nanosheets of hybrid CoFeO x /CPAs were promising OER electrocatalysts. Some of us recently [20] proposed that the high and durable electrocatalytic activity of a new 1D cobalt coordination polymer (Co-dppeO 2) is due to its highly disordered structure, giving rise to exceptional resilience. Further theoretical calculations and in situ characterizations proved that the key architecture behind the high OER activity was arising from the {H 2 O-Co 2 (OH) 2-OH 2 } edge-site motifs. This study demonstrated the high potential of low-cost Engineering low-crystalline and ultra-thin nanostructures into coordination polymer assemblies is a promising strategy to design efficient electrocatalysts for energy conversion and storage. However, the rational utilization of coordination polymers (CPs) or their derivatives as electrocatalysts has been hindered by a lack of insight into their underlying catalytic mechanisms. Herein, a convenient approach is presented where a series of Ni 10-x Fe x-CPs (0 ≤ x ≤ 5) is first synthesized, followed by the introduction of abundant structural deficiencies using a facile reductive method ...

Mechanistic insight into the active centers of single/dual-atom Ni/Fe-based oxygen electrocatalysts

“…Interestingly, the incorporation of Fe species demonstrates a typical “volcano”-type correlation with the OER activity (Fig. 3g ), which agrees well with previous works and recent studies on NiFe-based catalysts 45 , 46 . Specifically, the catalyst with the nominal Ni/Fe molar ratio of 7:3 displays the best activity with an overpotential of 270 mV at the current density of 10 mA cm −2 (Fig.…”

“… 44 . Inspired by the recent development of NiFe coordination polymers for high OER performance 45 , we here developed the NiFe-CNG dual-site SACs with the goal of notably improving the OER performance of the above single-site SACs. As expected, the addition of Fe species leads to a significant improvement of the OER activity of Ni-CNG (Fig.…”

Molecular and heterogeneous water oxidation catalysts: recent progress and joint perspectives

“…Overall, we noticed that the strategy of vacancy introduction is attracting increasing attention as an effective way to significantly improved catalyst properties, from exposing more surface sites to enhanced electrical properties. 239 However, fundamental questions, such as 'the more vacancies, the better?' and 'are vacancies stationary or mobile?'…”

Dynamics and control of active sites in hierarchically nanostructured cobalt phosphide/chalcogenide-based electrocatalysts for water splitting

“…High-surface nanomaterials are preferable targets for elucidating electrocatalytic interface processes. 53–56 Therefore, we constructed a series of hierarchical nanostructures of cobalt phosphide nanoboxes (denoted as Co–P NBs) and Fe doped cobalt phosphide nanoboxes (Co@CoFe–P NBs) from tailored coordination polymer precursors via a self-templating strategy. This controllable strategy furthermore brought forward single-shell cobalt sulfide nanoboxes (Co–S NBs), hybrids of cobalt sulfides and CoFe-based Prussian blue nanoboxes (Co–S@CoFe–PB NBs), double-shell CoFe-based oxide nanoboxes (Co@CoFe–O NBs), as well as CoFe-based selenides (Co@CoFe–Se), and CoFe-based tellurides (Co@CoFe–Te).…”