Metal-based electrocatalysts with different sizes (single atoms, nanoclusters, and nanoparticles) show different catalytic behaviors for various electrocatalytic reactions. Regulating the coordination environment of active sites with precision to rationally design an efficient electrocatalyst is of great significance for boosting electrocatalytic reactions. This review summarizes the recent process of heterogeneous supported single atoms, nanoclusters, and nanoparticles catalysts in electrocatalytic reactions, respectively, and figures out the construct strategies and design concepts based on their strengths and weaknesses. Specifically, four key factors for enhancing electrocatalytic performance, including electronic structure, coordination environment, support property, and interfacial interactions are proposed to provide an overall comprehension to readers in this field. Finally, some insights into the current challenges and future opportunities of the heterogeneous supported electrocatalysts are provided.

Design concept for electrocatalysts

CO2 electroreduction reaction (CO2RR) to fuels and feedstocks is an attractive route to close the anthropogenic carbon cycle and store renewable energy. The generation of more reduced chemicals, especially multicarbon oxygenate and hydrocarbon products (C2+) with higher energy density is highly desirable for industrial applications. However, selective conversion of CO2 to C2+ suffers from high overpotential, low reaction rate and low selectivity, and the process is extremely sensitive to the catalyst structure and electrolyte. Here we discuss strategies to achieve high C2+ selectivity through rational design of the catalyst and electrolyte. Current state-of-the-art catalysts, including Cu and Cu-bimetallic catalysts as well as alternative materials are considered. The importance of taking into consideration the dynamic evolution of the catalyst structure and composition are highlighted, focusing on findings extracted from in situ and operando characterizations. Additional theoretical insight into the reaction mechanisms underlying the improved C2+ selectivity of specific catalyst geometries/compositions in synergy with a well-chosen electrolyte are also provided.

Rational Catalyst and Electrolyte Design for Co2 Electroreduction Towards Multicarbon Products

The oxygen reduction reaction (ORR) is a key reaction for energy conversion and storage systems such as polymer electrolyte membrane fuel cells (PEMFCs). Studies on Pt and Pt-transition metal alloy single crystals have established that the ORR is best electrocatalyzed on bimetallic alloys and at (111) facets. Combining alloying and ensemble effects recently led to 20-30-fold enhancement of the specific activity (normalized per real cm 2 of catalyst) for the ORR on PtNi/C nanooctahedra relative to Pt/C nanoparticles. However, due to the highly oxidizing conditions of the PEMFC cathode, the stability of PtNi/C octahedra is poor in PEMFC cathode operating conditions, thus compromising their utilization in real devices. Strikingly, it also turned out recently that structurally-disordered PtNi nano-catalysts, such as hollow PtNi/C nanoparticles, dealloyed PtNi/C nanoparticles, PtNi aerogels or PtNi nanowires feature highly desirable and sustainable ORR activity (x 10-12 in specific activity relative to pure Pt/C). However, to date, the mechanisms of this unexpected ORR activity enhancement remain unclear, and prevent further development of this vital technology for a carbon-free energy future. To shed fundamental light onto these issues, state-of-the art PtNi/C nanocatalysts with distinct atomic composition, size, shape and density of disorder were synthesized. Their disorder was quantified experimentally, using the values of microstrain (a parameter accessible by the Rietveld refinement of wide-angle X-ray scattering patterns) that is representative of the local distortion of a crystal lattice. Thanks to ab initio calculations, the contributions of bulk and surface structural disorder were disentangled, and a new parameter, the surface distortion (SD), was established. The SD descriptor was used to rationalize the ORR activity enhancement of the two classes of materials (structurally-ordered and structurally-disordered), and to probe their stability in simulated PEMFC cathode operating conditions.

Surface distortion as a unifying concept and descriptor in oxygen reduction reaction electrocatalysis

Recent Advances in Complex Hollow Electrocatalysts for Water Splitting

Recent advances in the pre-oxidation process in electrocatalytic urea oxidation reactions.

Some serious challenges in energy and environment need us to find out the way that can solve them in sustainable process. There are many sustainable electrocatalytic processes which might provide the answers for above mentioned challenges, such as oxygen reduction reaction (ORR), water splitting, carbon dioxide reduction reaction (CO2RR) and nitrogen reduction reaction (NRR). These reactions can enhance the value-added to produce the hydrogen energy through water splitting, or transfer useless CO2 and N2 into fuels and NH3. These electrocatalytic reactions can be driven by high-performance catalysts. Therefore, it is one of important electrocatalytic fields to explore novel electrocatalysts. In this content, we need to discuss a varies of electrocatalysts for sustainable processes systematically, and further give insights on the status and challenges. This gives us the opportunity to organize the 2020 Roadmap on electrocatalysts for green catalytic processes and provide some suggestions for future researchers.

https://iopscience.iop.org/article/10.1088/2515-7639/abd596/pdf

Yuan Qiu

Papers

2021 Roadmap: electrocatalysts for green catalytic processes