Portable water splitting devices driven by rechargeable metal–air batteries or solar cells are promising, however, their scalable usages are still hindered by lack of suitable multifunctional electrocatalysts. Here, a highly efficient multifunctional electrocatalyst is demonstrated, i.e., 2D nanosheet array of Mo‐doped NiCo2O4/Co5.47N heterostructure deposited on nickel foam (Mo‐NiCo2O4/Co5.47N/NF). The successful doping of non‐3d high‐valence metal into a heterostructured nanosheet array, which is directly grown on a conductive substrate endows the resultant catalyst with balanced electronic structure, highly exposed active sites, and binder‐free electrode architecture. As a result, the Mo‐NiCo2O4/Co5.47N/NF exhibits remarkable catalytic activity toward the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), affording high current densities of 50 mA cm−2 at low overpotentials of 310 mV for OER, and 170 mV for HER, respectively. Moreover, a low voltage of 1.56 V is achieved for the Mo‐NiCo2O4/Co5.47N/NF‐based water splitting cell to reach 10 mA cm−2. More importantly, a portable overall water splitting device is demonstrated through the integration of a water‐splitting cell and two Zn–air batteries (open‐circuit voltage of 1.43 V), which are all fabricated based on Mo‐NiCo2O4/Co5.47N/NF, demonstrating a low‐cost way to generate fuel energy. This work offers an effective strategy to develop high‐performance metal‐doped heterostructured electrode.

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Capacitive deionization (CDI) is a promising cost-effective and low energy consumption technology for water desalination. However, most of the previous works focus on only one side of the CDI system, i.e., Na+ ion capture, while the other side that stores chloride ions, which is equally important, receives very little attention. This is attributed to the limited Cl– storage materials as well as their sluggish kinetics and poor stability. In this article, we demonstrate that a N-doped porous carbon framework is capable of suppressing the phase-transformation-induced performance decay of bismuth, affording an excellent Cl– storage and showing potential for water desalination. The obtained Bi-carbon composite (Bi/N-PC) shows a capacity of up to 410.4 mAh g–1 at 250 mA g–1 and a high rate performance. As a demonstration for water desalination, a superior desalination capacity of 113.4 mg g–1 is achieved at 100 mA g–1 with excellent durability. Impressively, the CDI system exhibits fast ion capturing with a desalination rate as high as 0.392 mg g–1 s–1, outperforming most of the recently reported Cl– capturing electrodes. This strategy is applicable to other Cl– storage materials for next-generation capacitive deionization.