Are there countries that bar nationals from traveling to certain countries? (Outbound travel ban)

Yes, there are several. Most famously, the United States bars travel to Cuba, although the strength and enforcement of the prohibition has waxed and waned, and if you want to split legal hairs it's not traveling that's prohibited, just spending money there.

Quite a few countries also try to ban their citizens from visiting Israel, with some countries like Bangladesh going so far as to inscribe the prohibition in their passports:

However, all these bans suffer from the same basic failing that you can't dictate terms to other countries: Cuba and Israel are happy to accept Americans and Bangladeshis respectively, and are even courteous enough not to stamp any evidence of visiting into passports.

The US bans the use of a regular US passport to visit North Korea. (You can get a special validation passport if you need to visit North Korea.) However, this doesn't technically ban US citizens from visiting North Korea per se, as it doesn't ban US citizens from using a different country's passport or other travel document to visit North Korea.

India bans its nationals from visiting Pakistan as tourists. Of course there are exceptions. Business visits, visits to family or for a pilgrimage are allowed.

North Korea bans their citizens from going anywhere outside North Korea in most cases.

As a side note, Wikipedia lists travel bans (but not reverse travel bans).

Australian law allows the Minister for Foreign Affairs to designate a declared area in a foreign country, making it a criminal offence for Australians to visit or remain in that area, punishable by up to ten years' jail.

This law was instituted out of concern over the prospect of Australians travelling to ISIS-related conflict zones and then returning home trained for terrorism.

As far as I know, this law has so far only been applied at province level (Mosul and al-Raqqa) and those designations have ended, but at the Foreign Minister's discretion it could be used to impose a travel ban on an entire country.

India has an "Emigration Certificate" system that bars its nationals from travelling on work visas to certain countries, unless pre-approval has been granted.

The background to this is that less-educated Indian citizens have been enticed to work abroad in menial jobs in countries with lax labour laws. Due to the pay differential for manual roles, this seems like an appealing prospect at first. However after landing at the destination they have faced bonded labour or slavery-like situations where they are not paid as promised, cannot leave (as their passport is confiscated by their employer), have to live in squalid conditions, under constant threat of arrest by local law enforcement.

To mitigate this, India has the "Emigration Certificate" system. Any Indian traveling with a work visa to United Arab Emirates (UAE), The Kingdom of Saudi Arabia (KSA), Qatar, Oman, Kuwait, Bahrain, Malaysia, Libya, Jordan, Brunei, Yemen, Sudan, Afghanistan, Indonesia, Syria, Lebanon, Thailand and Iraq, has to apply for and receive emigration clearance from the Indian government's "Protector of Emigrants" office. This has to be done weeks before the flight. Such workers receive pre-departure orientation about their rights and are registered with the Indian missions for any future assistance.

If Indians travelling on a work visa to those countries turn up at the airport without this clearance, they will be denied exit. India operates outbound emigration control at its airports for this purpose.

Indian citizens who have completed the 10th grade, are above 50 years old, or have lived abroad for three years, are exempt from this rule.

This appears to be fairly common, although it was more common in the past.

A number of countries bar their passport-holders from visiting Israel, sometimes with an inscription in the passport along the lines of "This passport is valid for all countries except Israel", or "This passport is valid for all countries except those listed in Exhibit A" (where Exhibit A lists Israel). Examples of such countries include most countries in North Africa, most countries in the Middle East, countries in South Asia such as Bangladesh and Pakistan, countries in South East Asia such as Malaysia and Indonesia, etc.

In the past, lots of countries barred their passport-holders from visiting the USSR, South Africa, China, Israel, North Korea, etc. It seems that Israel still remains one of the few widely-banned countries.

Saudi Arabia not only forbids travel to Israel, it even forbade aircraft traveling to Israel to pass through its airspace until just recently (March 2018 - only Air India).

Some countries have specific regulations that affect citizens that have specific classified knowledge by virtue of their employment. These ban or restrict travel to hostile countries. These bans can be open ended to such an extent that one list that I have seen includes countries that either now do not exist or have changed their regimes and are now friendly.