The sluggish kinetics of Oxygen Reduction Reaction (ORR) at the cathode in proton exchange membrane fuel cells or metal-air batteries requires highly effective and stable electrocatalysts to boost the reaction. The low abundance and high price of Pt-based electrocatalysts hamper the widespread application of proton exchange membrane fuel cells and metal-air batteries. As promising alternatives, metal-free carbon materials, especially upon doping heteroatoms or creating defects demonstrated excellent ORR activity, which is as efficient as or even superior to commercial platinum on carbon. Significant progress on the development of advanced carbon materials as highly stable and durable catalysts has been achieved, but the catalytic mechanisms of these materials still remain undistinguished. In present review, we summarized the up-to-date progress in the studies of carbon materials, and emphasized on the combination of experiment and theory to clarify the underlying mechanisms of these materials. At last, we proposed the perspectives on the proper strategies of elucidating the mechanisms of carbon materials as electrocatalysts towards ORR.npj Computational Materials (2019) 5:78 ; https://doi.

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The advancement of efficient electrocatalysts toward the nitrogen reduction reaction (NRR) is critical in sustainable ammonia synthesis under ambient pressure and temperature. Manipulating the electronic configuration of electrocatalysts is particularly vital to form metal–nitrogen (MN) bonds during the NRR through regulating the active electronic states of sites. Here, in sharp contrast to stable 2H MoS2 without metal chains, MoMo bonding in metastable polymorphs of MoS2 bulk (zigzag chain in the 1T′ phase and diamond chain in the 1T″′ phase) is discovered to significantly increase intrinsic electron localization around the metal chains. This can enhance the charge transfer from the adsorbed nitrogen molecule to the metal chains, allowing for boosted NRR kinetics. The electrochemical experiments show that the NH3 yield rate and the faradaic efficiency of the metastable 1T″′ MoS2 rich with abundant Mo–Mo bonds are about 9 and 12 times above average than those of 2H MoS2, correspondingly. Theoretical simulations reveal the high local electron density surrounding the MoMo chains and sites can promote π back‐donation, which is beneficial for increasing nitrogen adsorption, strengthening the MN bonds, and reducing the cleavage barrier of the triple NN bond.

Suppressing the Pt dissolution still remains a big challenge in improving the long‐term stability of Pt‐based catalysts in electrochemical energy conversion. In this work, the degradation of Pt nanoparticles is successfully suppressed via weakening the Pt–O dipole effect by adjusting the electronic structure of surface Pt atoms. The specially designed graphitic‐N‐doped carbon nanosheets with balanced N content and graphitization degree as well as fewer defects are prepared for anchoring Pt nanoparticles to enhance the electronic metal–support interaction. This can accelerate the electron transfer from Pt to substrate, decrease the surface electron density of Pt, and attenuate the Pt–O interaction. As a result, the rate of Pt dissolution decreases by 95% compared to that of commercial Pt/C toward the oxygen reduction reaction and thus the catalytic stability is significantly improved in the electrochemical accelerated durability test. The theoretical simulation shows that the inhibition of surface Pt dissolution is attributed to the enhanced energy barrier in the initial relaxation process.

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Serious challenges in energy and the environment require us to find solutions that use sustainable processes. There are many sustainable electrocatalytic processes that might provide the answers to the above-mentioned challenges, such as the oxygen reduction reaction (ORR), water splitting, the carbon dioxide reduction reaction (CO2RR), and the nitrogen reduction reaction (NRR). These reactions can enhance the value added by producing hydrogen energy through water splitting or convert useless CO2 and N2 into fuels and NH3. These electrocatalytic reactions can be driven by high-performance catalysts. Therefore, the exploration of novel electrocatalysts is one of the important electrocatalytic fields. In this paper, we aim to systematically discuss a variety of electrocatalysts used for sustainable processes and to give further insights into their status and associated challenges. We invited many famous research groups to write this roadmap with topics including platinum (Pt) and its alloys for ORR, oxides for ORR, chalcogenides for ORR, carbon-based hollow electrocatalysts for ORR, carbides for ORR, atomically dispersed Fe–N–C catalysts for ORR, metal-free catalysts for ORR, single-atom catalysts (SACs) for ORR, metal boride (MB) electrocatalysts for water splitting, transitional metal carbides (TMCs) for water splitting, transition metal (TM) phosphides for water splitting, oxides for water splitting, sulfides for water splitting, layered double hydroxides for water splitting, carbon-based electrocatalysts for water splitting, Ru-based electrocatalysts for water splitting, metal oxides for CO2RR, metal sulfides for CO2RR, metals for CO2RR, carbon for CO2RR, SACs for CO2RR, heterogeneous molecular catalysts for CO2RR, oxides for NRR, chalcogenides for NRR, C3N4 for NRR, SACs for NRR, etc. Their contributions enabled us to compile this 2020 roadmap on electrocatalysts for green catalytic processes and provide some suggestions for future researchers.

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