Practical electrochemical water splitting requires cost-effective electrodes capable of steadily working at high output, leading to the challenges for efficient and stable electrodes for the oxygen evolution reaction (OER). Herein, by simply using conductive FeS microsheet arrays vertically pre-grown on iron foam (FeS/IF) as both substrate and source to in situ form vertically aligned NiFe(OH) x nanosheets arrays, a hierarchical electrode with a nano/micro sheet-on-sheet structure (NiFe(OH) x /FeS/IF) can be readily achieved to meet the requirements. Such hierarchical electrode architecture with a superhydrophilic surface also allows for prompt gas release even at high output. As a result, NiFe(OH) x /FeS/IF exhibits superior OER activity with an overpotential of 245 mV at 50 mA cm −2 and can steadily output 1000 mA cm −2 at a low overpotential of 332 mV. The water-alkali electrolyzer using NiFe(OH) x /FeS/IF as the anode can deliver 10 mA cm −2 at 1.50 V and steadily operate at 300 mA cm −2 with a small cell voltage for 70 h. Furthermore, a solar-driven electrolyzer using the developed electrode demonstrates an exceptionally high solarto-hydrogen efficiency of 18.6%. Such performance together with low-cost Fe-based materials and facile mass production suggest the present strategy may open up opportunities for rationally designing hierarchical electrocatalysts for practical water splitting or diverse applications.

Strong metal–support interaction (SMSI), commonly happening between metal and metal oxide support, has drawn significant attention in heterogeneous catalysis due to its capability of enhancing the activity and stability of catalysts. Herein, the strong interaction between metal oxide and carbon supports is discovered to significantly boost the performance for electrocatalytic CO2 reduction reaction (CO2RR). A molecular engineering strategy is designed to develop undoped, N-doped, S-doped, and N,S-codoped porous carbon supports with similar physical properties (denoted as C, NC, SC, and NSC, respectively). These supports can host high-density SnO2 nanoparticles (over 60 wt. %) in a small size of ∼3.5 nm and good distribution, providing an excellent platform to understand the strong metal oxide–support interaction (SMOSI) and their influence on electrocatalytic performance. Systematic experimental and theoretical investigations discover the SMOSI between SnO2 nanoparticles and carbon supports in an order of SnO2/NSC > SnO2/NC > SnO2/SC > SnO2/C. Such SMOSI enables the effective electron transfer from carbon support to SnO2 nanoparticles, strengthening the adsorption of key reaction intermediate of CO2 •– and thus promoting CO2RR. With the strongest SMOSI, SnO2/NSC exhibits significantly enhanced selectivity and activity for CO2 reduction to HCOOH with a high faradaic efficiency of 94.4% and an extraordinary partial current density of 56.0 mA·cm–2 in an H-cell, outperforming the majority of Sn-based catalysts. Notably, SMOSI can simultaneously secure the active sites and thus remarkably enhance their catalytic durability, making it a promising strategy for exploring efficient and stable catalysts for diverse applications.

Nitrogen‐doped carbon materials (N‐Cmat) are emerging as low‐cost metal‐free electrocatalysts for the electrochemical CO2 reduction reaction (CO2RR), although the activities are still unsatisfactory and the genuine active site is still under debate. We demonstrate that the CO2RR to CO preferentially takes place on pyridinic N rather than pyrrolic N using phthalocyanine (Pc) and porphyrin with well‐defined N‐Cmat configurations as molecular model catalysts. Systematic experiments and theoretic calculations further reveal that the CO2RR performance on pyridinic N can be significantly boosted by electronic modulation from in‐situ‐generated metallic Co nanoparticles. By introducing Co nanoparticles, Co@Pc/C can achieve a Faradaic efficiency of 84 % and CO current density of 28 mA cm−2 at −0.9 V, which are 18 and 47 times higher than Pc/C without Co, respectively. These findings provide new insights into the CO2RR on N‐Cmat, which may guide the exploration of cost‐effective electrocatalysts for efficient CO2 reduction.