# Most-cited Energy papers of 2021, with free PDFs

The 25 most-cited Energy research papers published in 2021, ranked by citations in OpenAlex, with their original abstracts and free PDFs where available.

1. [Hydrogen energy systems: A critical review of technologies, applications, trends and challenges](https://nerdi.pages.dev/paper/W3159296886) · 2,340 citations
2. [Clean and Affordable Hydrogen Fuel from Alkaline Water Splitting: Past, Recent Progress, and Future Prospects](https://nerdi.pages.dev/paper/W3171647639) · 1,967 citations
3. [Emerging S‐Scheme Photocatalyst](https://nerdi.pages.dev/paper/W4200426529) · 1,958 citations
4. [Hydrogen production from water electrolysis: role of catalysts](https://nerdi.pages.dev/paper/W3128490572) · 1,523 citations · Free PDF
5. [CO 2 electrolysis to multicarbon products in strong acid](https://nerdi.pages.dev/paper/W3165555416) · 1,350 citations · Free PDF
6. [Nitrate electroreduction: mechanism insight, in situ characterization, performance evaluation, and challenges](https://nerdi.pages.dev/paper/W3162715248) · 1,316 citations
7. [Electrocatalysis for CO 2 conversion: from fundamentals to value-added products](https://nerdi.pages.dev/paper/W3132750624) · 1,298 citations
8. [Hydrogen Production Technologies: From Fossil Fuels toward Renewable Sources. A Mini Review](https://nerdi.pages.dev/paper/W3201768419) · 1,209 citations
9. [Interfacial chemical bond and internal electric field modulated Z-scheme Sv-ZnIn2S4/MoSe2 photocatalyst for efficient hydrogen evolution](https://nerdi.pages.dev/paper/W3133226951) · 1,119 citations · Free PDF
10. [Review on Ammonia as a Potential Fuel: From Synthesis to Economics](https://nerdi.pages.dev/paper/W3134967399) · 1,070 citations
11. [Hydrogen production, storage, utilisation and environmental impacts: a review](https://nerdi.pages.dev/paper/W3201994217) · 1,052 citations · Free PDF
12. [Recent advances in activating surface reconstruction for the high-efficiency oxygen evolution reaction](https://nerdi.pages.dev/paper/W3179766187) · 1,050 citations
13. [Advanced Transition Metal‐Based OER Electrocatalysts: Current Status, Opportunities, and Challenges](https://nerdi.pages.dev/paper/W3170651996) · 1,037 citations
14. [Advances and Challenges for the Electrochemical Reduction of CO 2 to CO: From Fundamentals to Industrialization](https://nerdi.pages.dev/paper/W3155378264) · 1,028 citations
15. [Tailoring Acidic Oxygen Reduction Selectivity on Single-Atom Catalysts via Modification of First and Second Coordination Spheres](https://nerdi.pages.dev/paper/W3162107883) · 1,010 citations
16. [Regulating Fe-spin state by atomically dispersed Mn-N in Fe-N-C catalysts with high oxygen reduction activity](https://nerdi.pages.dev/paper/W3136472111) · 1,002 citations · Free PDF
17. [Cooperative Coupling of Oxidative Organic Synthesis and Hydrogen Production over Semiconductor-Based Photocatalysts](https://nerdi.pages.dev/paper/W3189731110) · 977 citations
18. [An Inorganic/Organic S‐Scheme Heterojunction H 2 ‐Production Photocatalyst and its Charge Transfer Mechanism](https://nerdi.pages.dev/paper/W3159662645) · 908 citations
19. [How green is blue hydrogen?](https://nerdi.pages.dev/paper/W3193196963) · 908 citations
20. [Recent Development of Oxygen Evolution Electrocatalysts in Acidic Environment](https://nerdi.pages.dev/paper/W3138305217) · 903 citations
21. [Sulfur-anchoring synthesis of platinum intermetallic nanoparticle catalysts for fuel cells](https://nerdi.pages.dev/paper/W3206986155) · 901 citations
22. [Electronic metal–support interaction modulates single-atom platinum catalysis for hydrogen evolution reaction](https://nerdi.pages.dev/paper/W3163437048) · 892 citations · Free PDF
23. [Recent Advances in Design of Electrocatalysts for High‐Current‐Density Water Splitting](https://nerdi.pages.dev/paper/W3214949944) · 855 citations
24. [In situ Irradiated XPS Investigation on S‐Scheme TiO 2 @ZnIn 2 S 4 Photocatalyst for Efficient Photocatalytic CO 2 Reduction](https://nerdi.pages.dev/paper/W3199952910) · 844 citations
25. [Is There Anything Better than Pt for HER?](https://nerdi.pages.dev/paper/W3138383601) · 821 citations

Canonical page: https://nerdi.pages.dev/papers/energy/most-cited-2021