To realize future carbon neutrality, clean and sustainable electrochemical energy conversion and storage technologies are indispensable. Current devices include rechargeable batteries (e.g., Li-ion, Na-ion, and K-ion battery), fuel cells, and supercapacitors (SCs) that hold crucial positions in solving the current energy crisis and environmental pollution issues. [1][2][3][4] SCs and rechargeable batteries are the most popular electrochemical energy storage devices meeting future energy development demands. SCs usually possess high-power densities and long cycling lives but still suffer from low-energy densities. By comparison, rechargeable batteries have high-energy densities but still limited by lowpower densities, poor cycling stabilities, and short cyclic lives. Such tremendous differences in electrochemical properties between SCs and rechargeable batteries mainly originate from the differences in charge storage mechanisms. [5] According to the different charge storage mechanisms, SCs can be classified into electric double-layer capacitors (EDLCs), pseudocapacitors, and hybrid capacitors. [6,7] SCs made of carbon materials, such as carbon-based EDLCs, store electric charges at the electrode and electrolyte interface via physical adsorption/desorption of electrolyte ions. This process only involves surface reactions of ions without ion diffusion within the bulk electrode materials. [7][8][9] Pseudocapacitance often involves a Faradaic charge storage process by fast and highly reversible surface or near-surface redox reactions. Typically, pseudocapacitive electrode could be distinguished in underpotential deposition, redox reactions of transition metal oxides, and intercalation pseudocapacitance. [7] In most cases, functionalized porous carbons, such as oxygen-containing functional groups or heteroatomdoped carbon materials, have both EDL capacitance and pseudocapacitive storage mechanisms. Hybrid capacitors combine the advantages of EDLCs and pseudocapacitors, in which one electrode stores electric charge through battery-type faradaic process, while the other electrode stores electric charge based on capacitive mechanism. [10,11] Rechargeable batteries, such as Li-ion batteries (LIBs) and post-LIBs based on different charge carriers such as Na + and K + , store electric charges through intercalation, deintercalation, or adsorption of ions between the anode and cathode during charge/discharge processes. [1] For electrocatalysis, processes such as oxygen reduction reaction (ORR) in fuel cells and hydrogen evolution reaction (HER), as well as oxygen evolution reaction (OER) in water splitting, N 2 reduction reaction (NRR) and CO 2 reduction reaction (CO 2 RR), all often require high overpotentials and manifest sluggish kinetics in the absence of catalysts. The electrocatalytic processes usually take place according to three critical steps: 1) mass diffusion; 2) electron transfer; and 3) surface or interface reactions. [12] Generally, electrocatalytic ORR is a three-phase reaction and mainly includes two pathways:...

The oxygen functionalization of carbon materials has widely been employed to improve the catalytic performance of carbon-supported Pt (Pt/C) catalysts. Hydrochloric acid (HCl) has often been employed to clean carbons during the preparation of carbon materials. However, the effect of oxygen functionalization through a HCl treatment of porous carbon (PC) supports on the performance of the alkaline hydrogen evolution reaction (HER) has rarely been investigated. Herein, the impact of HCl combined with the heat treatment of PC supports on the HER performance of Pt/C catalysts has been comprehensively investigated. The structural characterizations revealed similar structures of pristine and modified PC. Nevertheless, the HCl treatment resulted in abundant hydroxyl and carboxyl groups and the further heat treatment formed thermally stable carbonyl and ether groups. Among the catalysts, Pt loading on the HCl-treated PC followed by a heat treatment at 700 °C (Pt/PC-H-700) exhibited elevated HER activity with a lower overpotential of 50 mV at 10 mA cm−2 when compared to the unmodified Pt/PC (89 mV). Pt/PC-H-700 also exhibited better durability than the Pt/PC. Overall, novel insights into the impact of the surface chemistry properties of porous carbon supports on the HER performance of Pt/C catalysts were provided, which were useful for highlighting the feasible improvement of HER performances by regulating the surface oxygen species of porous carbon supports.

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